I went with 20 percent all the way around and I drove through VA for 2 hours and got pulled over and given a tint ticket. I would not advise getting 20 if you live in VA.
now I had 20 percent put on but your window comes stock with factory tint. So my tint metered at 12 percent. I would go with 35 percent charcoal all the way around. But then again if I had to do it over again I would go with 15 percent tint, which would bring it down to like 7-8 percent. I like my privacy!
Jason
00 Audi S4, 2.7 Bi-turbo quattro

01 S10 Xtreme, 4.3l
98' Contour SE with some mods
96 Cavalier (beater)