I can safely say GC is the best version IMO.
The loading times are fairly similar..
The sound on Xbox is dolby digital but doesn;t seem to have been incorporated that well so even though better than GC it just doesn;t blow it away..
Control is rather similar with the Xbox version having identical default as Halo (which is a good thing) but the game feels a little clumsy. GC control is laid out in a similar manner using both analogue sticks but the game just feels better and more accurate when controlling..
Graphics the GC wins this particular battle. Seems to have more texturing (or could just be more polygons) but whatever it is it is noticeable. Another area GC wins is in the colour aspect of the game. The colours (as I said before) seem rather bright and almost primary, similar style to N64, whereas the GC version seems more subtle and have a certain realism to them. One thing I did notice on GC is there are a few slight frame rate issues when strafing, but not enough to worry about.
So final result is in my opinion the GC comes out on top...