I picked up a Works drop-in a few weeks ago, and tested it on the track this weekend. Works seems to flow better than the AFE drop-in I had been using before, but that might be my wishful thinking as it cost quite a bit more. If I ever get some reasonably priced dyno time, I will do a back to back test of Works vs AFE to see if there is much of a difference.
The Works filter itself is slightly smaller than AFE, making it easier to get into the airbox. It also comes with a metal bracket to keep it centered and tight. That's a big step up for K&N's crappy hard plastic bracket that had a tendency to break.
http://store.worksmotorsports.com/WO..._p/110.111.htm