There is ONLY one tint choice, IMO. Well, there are two, but one stinks and the good choice is expensive.
Formula One's "Pinnacle" film made by CP Films is what you want to get. It is a "ceramic" based film and will not interfere with GPS navigation, cell phones, AM, FM or satellite reception. It cost me $329 to have my "C" done, and I had to contact the manufacturer to find someone to do it - and they had to send the ONE GUY in my entire state the film!
The only other option is a "dyed" film. This is the cheap-o stuff that will turn purple.
Huper Optik is an architectural film that is "ceramic" based. There *ARE* places that say they install it on cars. But the rumor is that they LIE to customers and don't install the Huper on the (curved) rear window, and instead use dyed film for there. Huper is like $600 installed (read, ripoff).
I've had the Pinnacle now for 8 months and an very happy with it. It's the best tint I've ever had!