I used to work as a regional trainer for a national autoglass company so I've done more window tinting than I care to talk about.
I agree 3M is good stuff and is about the only brand that will guarantee against the tint turning purple after a few years.
Before they outlawed anything over 50% in Ohio, I had two layers of 95% on each window of the car I was driving at the time. My buddies and I would pull up next to cops at a stoplight and be drinking beer and he would never know because the tint was so dark. Ah yes, to be young and stupid again....
Make sure you go to a reputable place that has a certified installer working for them, that will offer a warranty if it tears, peels, or bubbles. I consider myself to be a very good installer even though I only do a few a year now and I've had to redo the door glasses on my wifes new Prelude twice now because of how tight the window goes up into the frame. So it pays to have a warranty.