The thing I pay most attention to is the change of color over time. I had 3M tint that was originally gray and over three years or so it started to turn purple. I hated that. When I got my next car, the 3M dealer said the new tint was improved but after three years, it too started to turn purple. My present cars don't have any tint on them since most of the gray tint I've seen on other cars that were at least several years old still show signs of them turning purple.
I'd like to know what brand of tint any of you have had for years that still is the same color now as it was when installed.