I'm going with B, all things unequal.
The main thing is, from your after tax account you only pay tax on the gains. If you need $10K, and have $10K in a fund with $5K of capital gains, you only pay capital gains tax on $5K. On an IRA withdrawal you pay ordinary income taxes on the full $10K. It's less of a hit to take from your after tax account unless your basis is $0.
On the other hand, if you're at all concerned with leaving something to heirs, your IRA will have to be drained by you or them at some point. But as the rules are today (subject to change), they would get stepped up basis on holdings in your after tax account, so it could be better to just hold onto those.
If charitable giving is a factor, consider whether it's better to do QCDs from your tIRA and giving appreciated assets. The latter relies on itemizing deductions.
Watch for any additional hits caused by taking more income, such as IRMAA, or causing more of your SS or QDivs/LTCGs to be taxed. That might favor taking from your taxable account to limit income.
There is no 15% bracket right now for regular income. I guess by "effective tax rate" you mean overall tax rate? That doesn't cover what the additional $10K (or whatever amount) you are taking, so I suggest using the marginal rate.
For the most part, it's probably not that much of a difference. But they aren't equal.