I own a 1995 C36 and overall it feels very solid. The problems common to these cars are head gasket, valve cover gasket, some electronic gremlins, and MAF sensor. I've read that some of the 5-speed trannies on the 1997 C36s and 1998+ C43s have problems. I love my C36, but if I had to choose between a C43 and C36 with the money not being a factor, I would definitely go with the C43. It's newer, has a better interior, and a V8!
Good luck and make sure to buy extended warranty.