Thanks for the responses. I specified in the beginning that I'm generally flying on a confirmed upgrade so having more F seats for a better upgrade chance is not significant to me. I've been paying attention to the seats lately and I have to say that I generally dislike the 757 seats for the two reasons people have mentioned: the headrests are too low and very uncomfortable in the lowered position (I try to get away with raising them a few inches but don't always succeed) and it's very hard getting in and out when the seats in the row ahead are reclined. On the other hand, I never watch TV on the plane either (if I did want to watch TV I'd just watch on my iPad), so I don't count that as a 737 advantage either. Overall, I guess I lean toward the 737 at this point. But it's interesting to hear the different perspectives.

UA recently lowered their M fare from EWR-SFO. I guess it's a benefit of VX competition. I am unlikely to fly VX even though UA can be a mixed bag, but it's nice to get the benefits of competition