Based on your post history you don’t need to worry about this for like 4 years.

From a strength standpoint, I think A is better given the higher frequency and less sets per exercise. From a hypertrophy standpoint, I think A and B are virtually identical given the equated volume. Having said that, since you're in a marathon training block, I'd go with B, as it leaves more days for running/rest.

Per the Pelland meta-regression (afaik the latest word on the topic), frequency doesn't seem to be a big independent factor (i.e., when volume is equated) for hypertrophy:

The primary meta-regression indicated an inconsistent dose-response relationship between weekly ‘fractional’ frequency and muscle hypertrophy, with a reciprocal model as the best fit and a 91.3% posterior probability the linear slope is greater than zero. While this indicates a potential slight positive effect of frequency, it should be noted that: i) the credible interval of the marginal slope was compatible with negligible effects, and ii) the contrast-based meta-analysis and two-stage meta-regression of only direct effects did not indicate an effect of frequency. In aggregate, our results suggest that any independent effect of additional frequency is small and is not consistently identifiable across modeling methods.

These results align with previous meta-analyses (19,111) and are most comparable to a 2019 meta-analysis by Schoenfeld et al. (14) reporting no significant effect of frequency in volume-equated studies utilizing direct hypertrophy measures (ES = 0.07 [95% CI: -0.08, 0.21]). The present meta-analysis utilizes additional data and bolsters the lack of a consistently identifiable independent effect of frequency on muscle hypertrophy. However, the 91.3% likelihood the linear slope is greater than 0 for the primary meta-regression, along with the wide uncertainty interval of the linear slope, permits additional study into the potential programming configurations (e.g., muscle group trained, training status, proximity to failure) that may elicit greater muscle hypertrophy with higher frequencies.

But it does seem to help strength (intuitively, higher frequency means more practice at the skill of lifting heavy):

The primary meta-regression indicated a positive dose-response relationship between weekly ‘fractional’ frequency and strength gains, with a reciprocal model as the best fit and a 100% posterior probability of the marginal slope exceeding zero. This, along with the contrast-based meta-analysis and two-stage meta-regression finding positive effects of frequency, indicates a dose-response relationship between frequency and strength gain. This finding is in contradiction to previous meta-analyses on the independent effects of frequency on strength gains (16–18) and adds additional insight to analyses reporting a significant effect (111). Across these previous meta-analyses, no consensus exists on the definition of frequency, and whether indirect training (i.e., exercises different from the strength assessment but training the involved muscles) counts towards weekly frequency has remained inconsistent.

The inclusion criteria and statistical analysis used in the present meta-regressions most closely align with a meta-regression by Grgic et al. (17), which reported no statistically significant relationship (p = 0.421) between frequency and 1RM strength gains in volume-equated studies. However, instead of necessarily different findings, the present meta-regressions build off of this analysis by exploring nonlinear models, a novel frequency quantification method, and additional data. Indeed, the effect size reported by Grgic et al. (17) increased notably from a frequency of 1 (ES = 0.53 [95% CI: 0.13, 0.93]) to a frequency of 2 (ES = 0.80 [95% CI: -0.25, 1.86]), which aligns with the increase seen in the control adjusted estimates for the reciprocal best fit model when increasing from a ‘fractional’ frequency of 1 (ES = 12.72% [95% CrI: 10.57%, 15.05%]) to 2 (ES = 17.32% [95% CrI: 14.34%, 20.56%]). Beyond this point, accelerating diminishing returns occur.

Higher frequencies allow for more frequent practice with the assessed exercise or a similar motor pattern. Indeed, simply practicing the test provides a robust stimulus for strength gains (118). The dose-response relationship found in the present meta-analysis indicates that additional exposures, and not simply additional sets, can enhance strength gains albeit with diminishing returns. Therefore, in addition to potential beneficial effects on muscular adaptations, it is possible that higher frequencies lead to higher quality practice, ultimately increasing training performance and therefore loads used (119). However, there is conceivably a point in which higher frequencies do not permit sufficient recovery and negatively impact training performance. Further research is necessary to investigate this.

It should be noted that the dose-response relationship between frequency and strength gains is limited to the training protocols used in the included studies. The average weekly ‘fractional’ set volume of 8.14 ± 6.23 in the included studies is relatively low; therefore, further analysis is required to explore the dose-response of per session volume and strength gains. Please refer to our parallel project for additional insight on the effects of per session volume (117).

Highly depends on your other focus. Don't give examples, tell us what your plan actually is...

If you're cutting, do 3 days. If you are running a marathon, doing 2 days and focusing on running is perfectly fine.

No need to be vague.

Adherence is still the most important principle. The problem with lower frequency vs higher frequency given equivalent volume, is the consequences of missing a session in a low frequency program are much greater, as its a higher percentage of total volume.

In engineering design this is called FMEA. Failure Modes and Effects Analysis - “If this fails, what are the consequences?”

Higher frequency seems to be better for beginners as it gets you more practice and exposure to stress when the loads are still low. As you get stronger it often necessitates more rest between sessions because you're moving more weight or doing more work as you get more fit and stronger. I work out once a week on average (not ideal, just what fits into my life) and my results are pretty decent. You can check my profile for proof.

3, consistent stimulus and you'll probably do more sets because you're done early and feel good.

If weekly sets and effort are matched, A vs B is basically the same for hypertrophy. Frequency on its own doesn’t seem to do much, it mostly just helps with practice and keeping set quality high. (Unless you're doing junk volume but at your volume it's fine)

Since you’re cutting and doing a marathon block, I’d pick B for recovery and just having more life. The best plan is the one you can actually hit hard consistently without your running falling apart. If you’re worried about losing muscle, I’d just bump the muscles that are only on 6 sets (chest, hams) up to 8-10 and keep those sets close to failure.

Personal note: I do BJJ & wrestling alongside lifting and when I dropped volume too low on a cut, I got weaker fast. Keeping it around 8-12 hard sets per muscle and hitting each muscle 2x/week worked way better.

This RP vid explains it well (not running but the same principle applies, cardio & lifting balance): https://m.youtube.com/watch?v=f8Vhi7SuFe8

When total weekly volume is on the lower to moderate end (up to ~16 fractional sets/week) then frequency likely doesn't matter much past 2x/week.

But, per the older frequency meta by Krieger and latest Remmert meta on per-session volume, there are diminishing returns the more sets you do in a single workout so spreading your volume out across more sessions may have a small positive effect if it allows you to keep your per-session volume at 8 sets or less.

So in your A & B example since both the weekly and per-session volume are both still on the lower end there probably wouldn't be much difference assuming adherence is exactly the same.

Frequency starts to matter more when you're doing more overall sets per week since it allows you to keep the per-session volume away from the more severe diminishing returns you start seeing past 8 or so sets in a single session.

Just note that the overall effect of frequency past 2x/week on muscle growth is likely pretty low according to the data we currently have. Though we don't have a ton of studies on very high volume like 20+ sets/week so it could have a bit more impact there extrapolating from the data we have on per-session volumes, but overall not likely to be a huge factor compared to the more important things like total number of sets and proximity to failure per set.

If you don't yet know how to use your strength, twice a week is better. You learn the movement patterns at the same time, and this is achieved through frequent repetition. You compensate for your lack of strength with higher frequency. Once you've learned to push harder and improved your level, you're able to do more volume per session, specifically reaching the minimum volume for hypertrophy and causing more "damage," hence the reduced frequency in favor of volume. You then need to think differently than with arguments about muscle recovery and the anabolic window of a few days, but rather in terms of tendon and nerve recovery, the latter becoming predominant in limiting progress in the medium term.

P.S.: In practice, people who split their training often perform much better than those who focus on high volume, except for very talented individuals.

I have this cake and plan to eat it. Should I cut it in 2 big pieces or 3 smaller pieces?

Once a week bro splits, too. 25 years ago, this was very popular with naturals and steroid users, and it worked well for both.