Mach 1 seats. I did a 10 hour straight drive the other day and my body felt fine after getting out of the car. The seats keep you planted in. Never felt that with either of the two Fox bodies I owned.
The SN95 seat have it over any of the stock Fox seats by leaps and bounds. Even your '96 seats should be a far cry more comfortable than the glorified milk cartons that used to come equipped in the old Fox's.
My Cougar seats are more comfortable than both of them though.
I don't know, my old '89 GT had the seats that would wrap around the sides of your legs and back with the turn of the knob. Plus, it had the piece to pull out to support your legs under your knees. They were pretty damn comfy if you ask me! But I do like the leather seats in my '02 as well, so .
'94-98 GT seats > '99-'04 GT seats
The cushion on the '99-'04 seats are flat as a pancake, while the '94-'98s have a lot more side bolster and look more like a race type seat.