Second to the above, Check your state and local laws! The cops have a hand held device that measures the tint of the glass, and if it exceeds it you get a 'fix it' ticket.

What I recommend is checking your state laws, then going to a professional and having the darkest % most reflective metalic tint installed you can legally have. The metalic tints last longer, are more resistant to scratches (but will still scratch), and most importantly reject the most amount of heat from the sun and keep the car cooler and the a/c working less hard. It appears that in Wyoming they allow you to go to any tint on the back and rear sides on an SUV, and 28% on the front windows. Check this link to look up your state laws:
State window tinting laws