I've searched and read a bunch of different posts and I still don't know which is more favorable. So let's vote. Also if you have first hand experience with any of them please post the pro's and con's. (FYI: Overkill tunes are no longer locked. The new versions can be edited with HP tuners.)
EDIT: TDCRacing brings up a good point. Please factor in customer service into your choice if applicable.