I can't comment on Kooks, but can on ARH. I went through several different sets of longtubes (Jet-Hot's, X-something or other bullshit brand stainless, etc.) before buying a set of ARH 1 7/8" race headers. Even though the ARH are larger diameter primaries than their predecessors, they fit so much nicer. No problems with them whatsoever and their Y-pipe fits great also. Either way, you'll win. Just pick one and go!

 

you shouldn't have problems with either one

 

i got the kooks with their true duals and its a awesome. only problem was my passenger side header was up against the k-member so i had to put a dent in it about 1/4" deep to clear and prevent rattling. Took lots of HARD hammering to get that dent in there. Other than that, awesome system and sound