If you just want the tinted look and don't mind the legality, a staggered 35% front/20% rear setup looks nice. I have this setup on my car, except with 18% rear (Suntek Carbon) and the rear windshield is 5% (installer ran out of 18%, oh well). I definitely would not recommend darker than 35% up front, though. If you have to drive through any dimmer areas (neighborhoods, rural areas, etc.) then 20% might limit your vision more than you'd like.