Which should I order?

APS is a true 3 inch throughout the entire system, and Cobb has bottlenecks so it can be mated to your stocker. After seein gone of the Cobb catbacks in person my mind was made up. If you want a true 3 inch system its a no brainer. Not to mention you can swap a cat in and out of the APS system where as the Cobb setup requires a completely different DP.

Seems like an easy answer to me