20% is NOT too dark. Best for balance of looks and visibility is 20% IMO. Looks nice and dark from outside, but still great visibility from inside. However, if you want to stay "legal" for NYC, go with 35% fronts and 20% for rears. It still blends well going from 35% to the 20% on the rears. Cetainly looks better than no tints on the fronts and 20% on the rears.

As far as reputable installers, I did mine in NJ. If you don't mind crossing the river, go to Top of the Line Tint in Lodi. Ask for Phil. Unbelievably professional job! (Ask for the 3M lifetime tint, never ever fades).