I like both. The 993 is a great driver's car, more than the M3.
But I think it's more difficoult to drive if you are not used to the rear mounted engine.
The M3 is more all around car, with a great engine(but be careful, it has problems that can be DANGEROUS, look here
http://www.auto-motor-und-sport.de/d/63711 and here
http://members.roadfly.com/jason/m3engines.htm
BTW, if the problem is fixed by the dealer, it's a great car, only the brakes are not so strong after hard use.
But remember, you can become a drift expert
PS: If you have the SMGII gearbox, and use it a lot in the fastest setting, you gearbo and differential will break very very soon :cry: