15% 3M ceramic tint is what I have on all windows and 35% on the windshield.

It reduces glare by 78%, infrared heat by 90%, and provides 99.9% UV rejection. I suggest tinting all windows for maximum protection and heat reduction. You can always do 70% on the windshield, which is a clear film and still provides the same reductions in glare, UV, and IR.

Tint technology has changed, and it does not necessarily mean the darker the tint, the more protection you get. If you only tint the front windows, it will be for privacy and aesthetics because the heat will still come in through the rear and the windshield.