#1 was R2c
#2 was Stillen Gen 3
... on my 2010 G37xS sedan with ERZ HFC and FI CBE.
Stillen has the best gains, without a doubt, but at the cost of a more difficult installation/fitment issues with the tubes/AC lines/frame. You shouldn't have to clean the filters until 50,000 miles, depending where you live. That's Stillen/K&Ns recommended interval.
Since you're looking for an easier install without any permanent modifactions to your car, go with the R2c system. They are the best SRI IMO. Best filters in the industry, sweet black nickel finish, and they have a very nice refined (yet loud) tone to them.