Just to make some points here.
The quality of the ride is determined mainly by the weather conditons, aided somewhat by the carrier's policy for avoiding weather (or not), and some contribution from ATC in routing.
The seats are nothing really to do with the airframe type, as it is up to the operator what to put in there - it's a bit like blaming your housebuilder for the comfort of your lounge chairs, to stick seat comfort on the aircraft builder.
Comparing say the A320 and the 737/757, the A320 is capable of giving better ambience as the cabin interior is 6" wider than the Boeings, which can correspond to a noticeable 1" extra width per seat, provided the carrier has actually bought seats to take advantage of this - Northwest (now Delta) put in the same seats in their A320s that they had in their 757s for the sake of spares standardisation, a real triumph by the engineering department over customer primacy. At least they got a 6" wider aisle.
The Tristar ? Yes, it's strange, but that always gave me an impression of elegant, quiet spaciousness as well, whichever operator, whose cause I used to try and work out but never was able to put my finger on. Something to do with the cabin ceiling proportions and the way the lighting was arranged seemed to have something to do with it.