Like focal said, the borla rocks!!. Has a nice exhaust note to it, is 2.5 inches with a 3 1/2 inch tip, the 2.5 inches is good if you are planning to do alot of engine mods. It's stainless steel and has a long ass warrenty. It sounds even better once you get the rest of your exhaust system done, I have the Ford racing header, Focus-Central high flow cat, Focus-Central flex pipe, and a Borla and the sound is just nice. NOT RICEY AT ALL!
MBRP also makes a 2.5 inch cat-back and is stainless steel too, those are also nice incase you wanna look into one of those, from what I've heard they have a rally sound to them.