Ha, tire doctor protection isn't an excuse for curb rash good sir.

 

i'd go with 30.. but it depends how dark you like your car. keep in mind if you have a dark colored car with dark interior most of the better tints (lumar) will appear darker to begin with.

i went 30 and don't regret it. a friend of mine went 30 on his car with dark interior and it looks like 15. i have wheat interior so mine is just right in terms of darkness.

its up to you tho.. i personally don't like the really dark look