OEM. It is better in every way. The power is just is good, filtering and time to clog is far better, it's cheaper, and the dealer can't blame any engine warranty claims on it. The ONLY possible benefits will be some intake whoosh, if you like that, and having it look different when you pop the hood.
Check out the following thread, particularly my post on the last page...
http://www.e90post.com/forums/showthread.php?t=137667