I second Will's comments. I was originally attracted to the jb3 due to the pricing. Ultimately, I switched because of the better feature set. Now, the gap has shrunk somewhat but Vishnu continues to implement new technologies all the time. Plus, it did feel a bit smoother. I also recently considered Cobb mainly due to the quick installation. But, they are new to the game. That means no meth support yet and a few snags with early 07 models (like mine). So it's Vishnu for me.
Btw, I'd recommend buying used. Seems you can get an unlocked one for $5-600.