Do a search on the forums, this one has been done to death.
quick answer: if you are after pure power, get the gze and stick a turbo on it, if you want a round town car, use the 20v. Its no that the 20v is bad, its just so many people have expected more out of it tht it can provide in stock form.
read up on both engines, and choose the one that suits the end result you want.