I go 35% on the two front windows, and 20% on all the rears. A couple of reasons I do this. The biggest reason is because I like to be able to see out at night, and 20% is just too dark to see through clearly at night. Also, 35% is legal on the two front windows, so you don't have to worry about having to remove it, should you get caught being darker than legal. With the rest of the windows being 20%, you can't even see that the front windows are lighter. My current Impala looks like it has 35% all the way around, and that's a little light, but still gets the UV protection, and that's the number one reason for tinting.