I like the placement better of the Stillen, but I like the fact that Injen has dry filters that require less maintenance. You will have to remove the front bumper every time you clean the filters.
I also like that Injen has a black finish as well, requiring less polishing and giving a stealth look IMO. I owed an Injen on my G35 and fit and finish are great.
Goog luck on your purchase!
