I prefer a fixed seat versus a suspension seat no matter what, but I like to really push my car in whoops and jumping. Too many accidents happen to people in suspension seats for me to risk it for my riding style. The only issue is there aren't really many seats available that fit the YXZ well as opposed to the suspension seats which have plenty of options.
The stock seats seem to be a good compromise for me. I haven't had a good reason to change them yet. They offer some cushion without bouncing you all over the place, and the riding position is better than most aftermarket.. My only gripe is they don't have the bolstering to hold you in like aftermarket seats do, but that's what harness are for.