Engage kind of tends to give you a lot of high statted units in the midgame that come at a good level and many are prepromotes. So a lot of the "best" units you won't get until later. There's also a fair number of units that are good primarily in the early game or that you will probably end up using early and drop later when you get better units unless you just like them and want to stick with them.
Some of my favorites that I like to use long term are Alear, Kagetsu, Merrin, Pandreo, Ivy, Hortensia, Panette, Citrine, Chloe, Seadall. Alear is of course your main character, but they also have decent stats and are one of the best holder for a lot of utility emblem rings like Byleth, Lucina etc. Kagetsu, Merrin, Pandreo, and Panette are units that join in the midgame and just have really good bases AND growths so they end up replacing a lot of early/mid game filler. They typically do want to be reclassed into better classes though. Ivy is a flying mage with generally good stats. She needs some help with speed buffs but otherwise she's a very strong magical carry. Hortensia is the best staffer in the game. Citrine has the highest magic stat and she can also make a good holder of utility emblem rings. She is slow but I still find her incredibly useful. You can also do weird things with her late game like reclass her to a bow class to abuse the overpowered radiant bow. Seadall is the dancer in this game so he's kind of a no brainer. Chloe is your early pegasus knight and one of the strongest early game character and she can easily carry you through the mid game. Her damage can fall off a bit after mid game but she can easily transition to a utility role at that point.
That being said, I want to shout out Vander, Louis and Yunaka for being really good up through the mid game when I usually drop them. Celine (if you promote her) or Framme can make a good staff bot until you get Hortensia. Sadly a lot of the other early recruits kind of just fill out your roster and then get replaced by better characters later.
Chloe is good through the game. I give her the first energy drop in jean’s prologue (building to the east) and she does a lot of work.
Celine is fine as a unit and then transitions into a decent backup staff user.
Jean is one of the best trainees in the series and can be literally anything pretty well because of his personal skill.
If you invest in Anna she can be a solid mage or a good bow user with the radiant bow. Miciah emblem on her lets her easily farm experience in the early game.
Citrine really wants a speed skill inherited from an emblem and she’s solid. Can also save scum for olwen’s bond ring for fire thunder.
Kagetsu is probably the strongest combat unit in the game, the only thing that holds him back is being a swordmaster on join.
Ivy is super over rated IMO. She’s tanky and fine but in my runs always lacks speed and damage.
Hortensia is a monster staffer.
Give Panette wrath and vantage with a crit forge weapon and she can solo most of the game after she joins.
Maybe a hot take but I really love timerra. She’s very held back by her skill being a proc.
Pandreo is VERY good.
Daggers are absurdly broken with how much value they get being forged. Yunaka is okay. Zelkov and Merrin are good.
I think its relative depending on which emblems and engravings you give certain characters. For me just went with characters I liked honestly each run ive played ive loved characters like Ivy especially if you give her a speedy emblem like Lyn, Diamant is good imo but maybe its just cuz Ive given him Tiki for a couple of runs I noticed the Starsphere can make any character good though, Kagetsu is a good unit, Alfred with the three houses emblem, Chloe is great, Liked Nel and Nil they can work with any emblem and the dragon classes are great also with more uses. Zelestia works well with Byleth or Chrom. I liked Goldmary as a tank.
Anyone is pretty decent.
Vander falls off a cliff (figuratively, he isn't Fates Kaze) but he's good the first couple of chapters and Bunet who joins later is just weak all around.
Other than these two you can use anyone you want without major drawbacks with the caveat that I wouldn't recommend trying to keep too many early game units around as Engage is a game where your investment matters and the earlier units tend to just take more of it.
Some characters notable for how fun they are:
Yunaka may fall off but if you get a good dagger early she's insane, also since you likely won't be doing your first playthrough on Maddening dodge-tanking is pretty cool.
Pannette is just built for vantage/wrath
If you have the DLC there's a character (you'll know when you get them) that can do some very stupid things with Emblem Soren
If you're playing on a difficulty below Maddening, invest in Yunaka. Give her Corrin's ring and a forged steel dagger with an engraving that raises crit rate. She can spend every turn setting up fog with Corrin's Dragon Vein ability, which activates her personal skill and boosts her crit even further and also makes her practically impossible to hit by anyone who's not in a Mystical class. She was 100% the MVP of my first run on Hard mode, but this setup doesn't really work on Maddening because Maddening enemies won't attack your units if they have a 0% hit rate.
i think it's really easy to get characters to be good in this game, to the point where you can pretty much use whoever you want, but my favorites unit wise that always turn out cracked are alcryst, kagetsu, & pandreo (the only one i reclass, making him a sage just maximizes his dmg output).
chloé and louis are extremely worth investing in too, they've always turned out good for me. but again you can make almost anyone good with the right investment+emblem comp. i love alfred and cèline who both famously fall off and cant keep up with other later units but i still brute force them and usually use all of my stat boosting items on them because i love them lol.
omg i just realized i also forgot goldmary. kagetsu pretty much dominates the sword user space but honestly i would say my second most reliable after him has always been her. she's tanky but not slow and always ends up turning out better than diamant for me
By my understanding every unit is good.
Guy called Bunet:
I also experienced this, but why lol
Bunet exists
Bunet is the only unit that's bad in my experience. Use whoever you think is cutest
Engage kind of tends to give you a lot of high statted units in the midgame that come at a good level and many are prepromotes. So a lot of the "best" units you won't get until later. There's also a fair number of units that are good primarily in the early game or that you will probably end up using early and drop later when you get better units unless you just like them and want to stick with them.
Some of my favorites that I like to use long term are Alear, Kagetsu, Merrin, Pandreo, Ivy, Hortensia, Panette, Citrine, Chloe, Seadall. Alear is of course your main character, but they also have decent stats and are one of the best holder for a lot of utility emblem rings like Byleth, Lucina etc. Kagetsu, Merrin, Pandreo, and Panette are units that join in the midgame and just have really good bases AND growths so they end up replacing a lot of early/mid game filler. They typically do want to be reclassed into better classes though. Ivy is a flying mage with generally good stats. She needs some help with speed buffs but otherwise she's a very strong magical carry. Hortensia is the best staffer in the game. Citrine has the highest magic stat and she can also make a good holder of utility emblem rings. She is slow but I still find her incredibly useful. You can also do weird things with her late game like reclass her to a bow class to abuse the overpowered radiant bow. Seadall is the dancer in this game so he's kind of a no brainer. Chloe is your early pegasus knight and one of the strongest early game character and she can easily carry you through the mid game. Her damage can fall off a bit after mid game but she can easily transition to a utility role at that point.
That being said, I want to shout out Vander, Louis and Yunaka for being really good up through the mid game when I usually drop them. Celine (if you promote her) or Framme can make a good staff bot until you get Hortensia. Sadly a lot of the other early recruits kind of just fill out your roster and then get replaced by better characters later.
Uh.
Chloe is good through the game. I give her the first energy drop in jean’s prologue (building to the east) and she does a lot of work.
Celine is fine as a unit and then transitions into a decent backup staff user.
Jean is one of the best trainees in the series and can be literally anything pretty well because of his personal skill.
If you invest in Anna she can be a solid mage or a good bow user with the radiant bow. Miciah emblem on her lets her easily farm experience in the early game.
Citrine really wants a speed skill inherited from an emblem and she’s solid. Can also save scum for olwen’s bond ring for fire thunder.
Kagetsu is probably the strongest combat unit in the game, the only thing that holds him back is being a swordmaster on join.
Ivy is super over rated IMO. She’s tanky and fine but in my runs always lacks speed and damage.
Hortensia is a monster staffer.
Give Panette wrath and vantage with a crit forge weapon and she can solo most of the game after she joins.
Maybe a hot take but I really love timerra. She’s very held back by her skill being a proc.
Pandreo is VERY good.
Daggers are absurdly broken with how much value they get being forged. Yunaka is okay. Zelkov and Merrin are good.
I think its relative depending on which emblems and engravings you give certain characters. For me just went with characters I liked honestly each run ive played ive loved characters like Ivy especially if you give her a speedy emblem like Lyn, Diamant is good imo but maybe its just cuz Ive given him Tiki for a couple of runs I noticed the Starsphere can make any character good though, Kagetsu is a good unit, Alfred with the three houses emblem, Chloe is great, Liked Nel and Nil they can work with any emblem and the dragon classes are great also with more uses. Zelestia works well with Byleth or Chrom. I liked Goldmary as a tank.
Anyone is pretty decent.
Vander falls off a cliff (figuratively, he isn't Fates Kaze) but he's good the first couple of chapters and Bunet who joins later is just weak all around.
Other than these two you can use anyone you want without major drawbacks with the caveat that I wouldn't recommend trying to keep too many early game units around as Engage is a game where your investment matters and the earlier units tend to just take more of it.
Some characters notable for how fun they are:
Yunaka may fall off but if you get a good dagger early she's insane, also since you likely won't be doing your first playthrough on Maddening dodge-tanking is pretty cool.
Pannette is just built for vantage/wrath
If you have the DLC there's a character (you'll know when you get them) that can do some very stupid things with Emblem Soren
If you're playing on a difficulty below Maddening, invest in Yunaka. Give her Corrin's ring and a forged steel dagger with an engraving that raises crit rate. She can spend every turn setting up fog with Corrin's Dragon Vein ability, which activates her personal skill and boosts her crit even further and also makes her practically impossible to hit by anyone who's not in a Mystical class. She was 100% the MVP of my first run on Hard mode, but this setup doesn't really work on Maddening because Maddening enemies won't attack your units if they have a 0% hit rate.
i think it's really easy to get characters to be good in this game, to the point where you can pretty much use whoever you want, but my favorites unit wise that always turn out cracked are alcryst, kagetsu, & pandreo (the only one i reclass, making him a sage just maximizes his dmg output).
chloé and louis are extremely worth investing in too, they've always turned out good for me. but again you can make almost anyone good with the right investment+emblem comp. i love alfred and cèline who both famously fall off and cant keep up with other later units but i still brute force them and usually use all of my stat boosting items on them because i love them lol.
& happy cake day! :3c
omg i just realized i also forgot goldmary. kagetsu pretty much dominates the sword user space but honestly i would say my second most reliable after him has always been her. she's tanky but not slow and always ends up turning out better than diamant for me