Go with InMotion, they were great to work with. If you don't want to mess with sending off the ECU, give them a deposit, they send you the tool to hook up your laptop, read the ecu, email them the file, they send you back the "tuning" file in a few hours, and you write it to the ecu (takes just a few minutes). That's how I did mine, and the difference was even noticeable to my girlfriend from the passenger's seat. I also use some 100 octane unleaded racing fuel 50/50 with the crappy premium here in Phoenix, and really tell the difference.

Just did a track day at PIR with a guy who used to own an Xfire, and he couldn't believe the difference (MB V8 instake with K&N's, InMotion chip, and Magnaflow exhaust).