The 737 seats in coach most closely resemble park benches.
The 757 in row 7ABC (ex-Continental plane) have no seat in front of you, so you've literally got more legroom than the people in First.
the ex-United 757's, I think the same is true of row 8. Check seatguru on that.
My vote is 757, even though I love the 737 mechanically.