depends what you are looking for. if you just want sound then get a flowmaster 40 series and pipe arrangement of your choice. 45 out the back, side swept, straight out the back, stock. (round 250) if you want performance and sound you should do headers back, but thats gonna cost you.
I prefer Borla myself, even though it is a little on the pricey side. I purchased and installed a Split-Rear Exit Cat-Back System on my 1995 3kgt about 6 months ago and it's been wonderful. Nice, deep rumbling sound. I got about 11 BHP ever since I installed it as well. I know it's expensive, but it is by far worth the $$$ you rake over.
i say go gibson or basani. imho they sound the best and the basani is gona put out a really nice hp gain. Don't do something custom unless you have heard the setup before or you just want to take a risk.