I have propedestals on my passenger bench. I can't give you a legit answer on whether they are better then a seaspension seat. I have ridden in the bench for a little while but they aren't as active as the seaspension on my drivers seat. Honestly they really can't be as they are a tandem set coupled together by the bench.
One thing to be aware of is the fact the suspension are on opposite ends. The propedestal has the action at the top. This means a foot rest clamped on the pole doesn't move with the seat. The seaspension has the action at the bottom therefore a footrest clamped around the pole moves with the seat.
I have both brands on my boat. The propedestal does work out better for the bench because the tube/shock extends through the floor. This allows for a lower seat.