I was in the same position as you a while ago I couldnt decide how dark to go. I was also concerned about insurance and all the rest. Do a search and you will find the thread on here, you may find it interesting.

I ended up going 20%, which is really 17% because of the factory 3%. I find it a bit too dark at night when reversing and for good visibility. In daytime I think it is just about perfect. If I had to do it again I would consider going to a 25% tint, which is what I originally wanted but they didnt stock 25% so I said f**k it ill just go with 20%. I definately would not do 35% its too light.

In the end I did tell my insurance I had window tinting but they didnt ask how dark and I didnt tell them either.