afe stage 2 filters better but gives slightly less HP is my understanding.
airhammer gives you highest hp gain with afeS2 being the second best.
everyone ive talked to hates k&n because their filters are the worst quality and they let more particles thru than almost all otehr filter brands. not to mention they dont even give the best horsies.
go over to www.lxforums.com
find the forum section called MFO Mods Face Off. it has a bunch of threads about cai's and comparisons, they have some guys doing this all on the same cars showing gains and losses comparitively. its a great message board everyone needs to read. its VERY well thought out testing.
Just installed my Airhammer yesterday and it looks and sounds awesome...performance wise, I have nothing to compare it to..but if we use the lx forums charts then its doing ok .I work 2 jobs , I got a little extra coin so I went with the Hammer.