I've used Formula 1 and liked it. Like Armored said, it ceramic. I personally feel that is a great thing. Both metallic and ceramic can somewhat decrease the sensitivity of your remote.
I have Huper Optik on my current cars (WK2 is ordered). If given the chance, I have searched out Huper Optik dealers after getting a car tinted with it from then on. It has crazy heat rejection that no one else can match at the moment. That said, from what installers have told me, it is difficult to install well because it is not quite as flexible as most tints. GC's shouldn't have an issue, but the rear window in my old 944 would have been a bitch.
Also in reading the forums and GC's manual (yes I'm chomping at the bit for mine to get here!), the windows that come tinted on the GC have little IR and almost no UV-B rejection. It could need further tinting/non-tinted film to reject it.
I am here: http://maps.google.com/maps?ll=32.852985,-96.813398