Very good point. It also has a lot to do with how much you are willing to deal with as an individual.

 

Just got 35% on the four windows and 20% on the rear windshield today. Honestly, beyond cops or the outside appearance, anything darker than 35% will be hard to see out of at night. I had 20% on my last car and if it's raining out at night, it's almost impossible to see what's to the side of you, or street signs, etc. The 35% is dark enough during the day to notice the difference but light enough that it's practical. Also, I've never had any issue with 35% on a car I had a few years ago as far as cops go.

I think your best bet is 35% all around!