On the MD-80, 3F (bulkhead) has more legroom than the non-bulkhead window seats. So much that the person in 3E doesn't need to get up if you wish to get out, even if both of you are large. To me, this is a big advantage of this seat over over window seats.
OTOH, 3A has less legroom than the non-bulkhead rows. I can get out to the aisle without making the person in 3B get up, but I couldn't do that when I was fat.
Haven't been on an AA 738 yet, so can't comment.