Hmmm - We could get really technical here about pixel density vs image quality but at the end of the day (and in my previous life in Film and TV) we always used to say "Content is King" - basically, its more important to capture good subject matter and frame it well rather than get too wrapped up in the technical merits of the video or photograph.
I've seen some brilliant photographs taken with a disposable camera and conversely, a friend of mine (with more money than sense) takes rubbish pictures with a Canon 5D Mk3!
So, why choose a GoPro?
I've got a Hero3 Black Edition - all singing and dancing - Hi-Res 4K images etc., etc. but the reality is... I'll probably never ever use that mode, nor will I probably ever use it to shoot 1080p at 60fps (incidentally - I've said this before, but in the UK and Europe we should be shooting 50fps and NOT 60fps - thats for NTSC - we're PAL).
What we need to ask ourselves is why? - what do we want the camera for? - I think 95% of people on this forum want their cameras to fix to their quads, take some great aerial footage and then share it on YouTube - and for this purpose, the best settings you'll ever need is 25fps 1920x1080 - even then, 1280x720 is still good enough. OK, if you want super sharp slo-mo, then a higher frame rate will achieve that.
The big problem you hit with shooting mega high quality video is editing it - once you start using the higher resolutions you're going to need a powerful computer and some really fast AV drives to handle the data rate (unless of course you compress the video and then you're dropping the quality!).
OK - I'll witter on for ever on this and get very boring - so why do I like GoPro Hero 3's (I don't like the Hero 2 too much though)
1. yes, the quality is really good for is relatively low cost
2. Spares are readily available (if you crash and break the lens you can find a replacement)
3. You can change the field of view (Ultra wide, Medium, Narrow)
4. Built-in Wi-fi - absolutely brilliant! - you can change all the setting and frame your shots - from your phone! - what other comparable camera does that?!
5. Its small - its light - perfect for strapping to a small quad
6. Finally, its got good 2nd hand value if you decide to change it for a newer model (Hero 2's are still selling well) so the actual cost of owning a GoPro is the difference between what you buy it for and what you sell it for (if you ever do!).
But am I happy strapping a GoPro to my Quad? Still a difficult one to answer! - I know I'll get better images from a GoPro but its still not an 80 quid camera.... Oh. all right... yes, I'll do it - shove the GoPro on the quad and pray!
Wow - I really could go on for ever about this (can't you tell its a subject close to my heart?) - but I won't.
Buy a GoPro!