The best exhaust would be one that flows the best. Usually that would mean running test pipes and high flow mufflers. But then , it would also, increase your noise level. If you are going for something that will pass smog or a visual inspection, gut your cats out. This is not legal, but it will improve your airflow. Search around for some exhaust kits that are built systems that are also carb legal. Many of the larger companies have CARB certification, this means if you get pulled over, you show them the certificate and the exhaust is deemed legal. You don't want to be getting exhaust tickets all the time, they are costly and a pain in the ***. You have to remove your entire exhaust (think: labor costs) then you have to get them signed off. Then if you want, put it back on and get pulled over again.

 

I depends on the emissions laws in that state but you might be able to pass with only one cat for the visual inspection. You can gut the cat but cats don't really hurt performance that much. I've seen only a couple horsepower gained from removing a cat. As far as exhaust systems, you could get the Greddy Evo. It will pass noise ordinance (94 db) and (with at least one cat in place) it should pass emissions.