keep it as dark as you legally can.....you wont get hasseled and ticketed...and youll still be able to see out at night enough not **** **** up.
durring the day it wont see that dark , but at night itll seem hella dark....ive done both 5% and 20% and hands down go wih 20. nothign ***** worse than not beign able to see a god **** ting when you backup at night