Just make sure the Seat cushion is supportive and doesn’t collapse the minute you sit on it. By far the best IMHO is the Milo gel seat which also features on the Quad box and Colmic, Trabucco ones. The Rives are generally rock hard or over soft, the newer seats by preston and the rest now have better cushions than before.
The other main thing to get right on any box is the distance from the footplate to the top of the seat, such that your able sit upright with your feet flat on the plate and the angle at your knees is 90deg and your thighs are parallel to the seat. That way your back is not going to be strained.
The reason most of us suffer from bad backs due to fishing is poor sitting posture. Pole fishing makes the problem even more irksome as there is a tendancy to sit with a curved spine leaning into the side the pole is used. So a correctly set up bump bar is also a consideration when buying a new seat.
You need to get to a big enough shop or ask your fishing buddies for a try on theirs and sit on as many different makes as possible.
My personal choice has been Milo and the box I have has been used virtually twice a week for the last 10 years and is still solid with no problems such as slipping leg grips that you get on others.