I like Full cat-backs for the simplicity of mixing and matching and imo its just cleaner. I would say Magnaflow. I have an SLP system on my 99 GTP and its a little raspy at high rpm + SLP parts you'll have to source as they dont make em anymore. Magnaflow your guaranteed a high quality system with a clean look and nice sound but your going to be paying a little more. Dynomax I have no opinion on, but they have also been around for a while and is a popular system for these cars.