I love the GC, I also own a PS2. Heck out of me and my roomates we have a combined 3 PS2s, 2 GCs, 1 X-Box, 3 GBAs, and well ofcourse 3 PCs. ^^
Having played all 3 systems this is how feel, graphically GC and X-Box to me are equal. So many people over look the beauty/quality of graphic's that little cube has when they compare it to the massive X-Box. Really I have yet to see anything on X-Box that looked worse on GC. However the PS2 unfortunately lacks, when there are games that come out for all 3 consoles, you can play the PS2 version up against the GC version, the GC version comes out far superior as does X-Box.
As far as controls go, I say PS2 wins hands down. Their controllers are the easiest to use, and simply have the best set up to work with your hands. I find the X-Box controllers to be a little on a big side, I consistantly have problems when I need to hit the start button or the black & white buttons due to thier location, It takes some getting used to, which is not fun; doable but not slick/comfortable. GC are kind of the opposite, though they arent too bad, Nintendo knows how to make consoles. I just find the standard controller to be well.. too small, buttons are all bunched up (my hands would get cramped up after playing a game for a little while). I had one of the big MadCatz controllers for a while, it was great, till it just stopped functioning one day. I now use a WaveBird controller, and ah.. its so much better.
I'm not even going to get into game selections as that is pretty much dependant on what you enjoy playing. GC has Nintendo's impressive allstar character's games. PS2 definately has the edge on RPGs. And well, X-Box has its own impressive library as well. ^^