I've got OEM GT3 seats in my C2, I bought them from someone on Pistonheads and they had been fitted to a 993 before, so the seats fitted fine. They are trimmed in marble grey leather, which matches my car's interior colour and they look absolutely awesome. I just did a 2000 mile trip around France and they were very comfortable and of course, held me in very well around the twisty bits. They are, of course, not as comfortable or easy to get into as comfort seats, but if you ever do track days or drive around bends "˜enthusiastically' then you will be very glad you bought them. I can confidently drive much faster around bends since having them fitted and they generally make me much more relaxed behind the wheel.
The comfort and 95-on sports seats are, in my opinion, crap for sporty driving. Of course, the GT3 seats don't recline so just get the one seat if you need access to the rear.
The fitting was hampered by missing bolts for the seat belt buckle recievers and this proved to be a pain in the a*** to and the whole thing probably took me 7 hours, spread over a month or so. It took a while to find a parts supplier who knew what I was talking about and I still had to file the bolts down to make them fit. The seats went in and out many times whilst I was learning what goes where, making mistakes, trying out different things etc. To be honest, it was a real case of trial and error and in spite of asking a few experts I never felt confident about their advice so ended up working a lot of stuff out myself. Having said that, I can't imagine anyone else taking longer as I'm a complete mechanical numpty.
There is no adjustment possible for seat height or rake but they all seem to be set fine for me, even though I'm 6'4" with long legs. A big plus for me is that the seat cushions are velcroed on so I can remove them for track days when I may not fit in with a helmet on.
If you want minimum hassle then go to somewhere like Southbound motor trimmers who will supply, trim and fit the seats for you. They may also size you up in order to put the rights amount of trim and padding.
I had previously bought a set of designtek seats which sat in the loft for ages I never tried to fit them and ended up selling them when I bought the GT3 seats. They don't feel as rigid and they looked like they would be a bitch to fit in the car, so I never bothered.