I dunno about the 737s -- living in AUS and IAH, I don't really have to deal with them so much on long flights. 777s and 767s to LAX, EWR, and all transpac/transatlantic destinations. 757s to lots of destinations, and I've got no complaints.

Like I said, I don't have much experience with the 73s on long flights, but I find the next gen 737s to be very nice. The furthest that I've taken a 73 is a 737-800 to LAS, which is about half the distance of LAX-EWR.