After the LTs and HF cats, it really depends on the type of sound and volume you are looking for. For example, a Borla ATAK catback system is loud and raspy....a Stainless Works Retro Chambered catback is loud, deep, and rumbling. On the other end is something like a Borla Touring is just slightly above stock. There are many quality systems out there. You just need to listen to as many as you can, in person if possible, and pick what you like.
Keep in mind that all systems will be amplified by LTs anf HF cats. Check out the exhaust sticky with a good set of ear buds to get some ideas.
Kooks 1-7/8 LTs; Calico coated w/HFCs, Solo Mach XL catback w/J-pipes, VMax TB, C.A.I. Intake, JRE Tune, RX Catch-Can