Best. I would'nt know.
Its like others have said. It depends on how far you want to go with your car in terms of mods.
The thing about the COBB AP....which I have and love. 2006 WRX stage 2 w/ cobb dp. Yeah!
Ok. The thing about COBB AP is they tune there maps to be used with specific parts. If you don't mind going their path life is great.
Even that said. You can always get a Protune.
I love my AP because Its easy to remove incase I need service at the dealer. And COBB parts and customer service are the tops.. That helped me make up my mind on who to go with.
I've had both my REX's with COBB parts and their AP and I would recommend it to anyone who wants EM but also likes the freedom of removing it when they need to.