Go with 2.25" duals into dual cats with either an H pipe or - for better performance - an X pipe between the cats and dual 50 series delta flow Flowtech mufflers. Go to their site
http://www.flowtechmufflers.com and check out the 50 series mufflers. They have some sound clips that will show you what they sound like (take into account the examples are of camaro 3.8L's). I truly believe you will not go wrong with the flowtech decision and 2.25" exhaust all the way. Going with a 3" single exhaust will only impede your air flow and reduce your back pressure too much. Besides, a 3" pipe only allows about 66mm of airflow to exit. If your throttle body is a 70mm, you have a 4mm restriction before you even start the car! If you go with dual 2.25", you have a total of 4.5" of exhaust room, giving about a 99mm airflow availability. If you are running a 70mm TB, you have an extra 29mm of room for your blower! With the delta chambers, you will still retain your back pressure since there's not a "direct" output (or straight-pipe). Too much flow is as bad as too much restriction.
Go dual and GET IT ON BABY!