What determins the quality of an HDMI cable and how good the lenght is?

Hut he issue might not be related to the cable but the output power the GoPro output which might decline over longer distances. What distances are you talking about.
There are HDMI transmitter/receivers that might be what you want.
Another option is to get a hdmi 2x1 or similar that have their own DC power to effectively extend/power the HDMI signal for a longer distance..
Presumably you are talking for distances more than the 3 or 6 feet (1 or 2 m)?

I haven't tried anything yet. Just trying to learn the best options.  Are you telling me the quality of the cable is not as important as how much power a camera puts out?
Thanks
Art

Look at hdmi 1.4 support and the throughput/quality.
I.e can handle larger amount of data throughput.
What is the range of distances you are looking at >12 feet?

See whether the camera includes specs for hdmi port distances spec

I want to run between 25-50 feet.  I have seen HDMI cables advertised 100feet but I heard you couldnt run a Go Pro camera that long:

http://www.videoguys.com/newtek-tricaster-mini-hdmi-cable-kit.html

I have SDI cameras that I can run a long ways, if I can run my Go pro cameras 100 feet I would be fine

If you're stuck with that kind of distance consider HDMI over Cat 5 or 6 Ethernet cabling