the side mount ones, which basically comes down to intentions. If you intend on going big HP#'s, then the FMIC is widely chosen. If you intend on going mid range HP and prefer to keep the stock plumbing then the side mounts are your best bet. You have to take into account core sizes, # of fins for cooling, availability of air flow to cool the intercoolers is a must also. I always like the Stillen ones but too expensive in my opinion. Really they all get the job done, but I can't recall a comparison between all of them. Figure out your needs and intentions for your Z, then fiqure out how much cash you'll need to dish out. Good luck.
