So long as you choose one of the premium tints, you'll be happy with heat rejection, no fading, and nice looks without the interference of a metallic film that interupts cell/radar/other electronics. Compare the heat rejection and you'll see they are all similar at this quality level.
It is also helpful to see the tint manufacturer options and grades of light side by side mounted to a white board so you can personally see any color bias. Your red vehicle will look really sharp with the tint contrast.
Most importantly, find a good installer with a clean facility that manages dust well and uses custom machine cutting for templates. Those who hand cut film, no matter how skilled, can cut into the glass, paint or clear coat quite easily. If you are also doing a clear bra (recommended), note the A7 front bumper is very intricate and complicated, and the machine cut film helps get this right.
The Huper is spectacular, but it is particularly fussy due to its thickness and only so many dealers have the installer skill set to lay it down correctly. 3M Crystalline is also moderately thick.
^thanks chenthu. still snowing here, spring fever setting in.
'13 Audi S7 (Expected 01/07/14)
2006 VW Touareg (gone)
2000 Audi A6 2.7T (gone)
1994 Audi 90CS (gone)
1986 Audi Coupe GT (gone)