Well I know that if all I had to choose from was either a Game Cube or a PS2 I would definately choose a Play Station2, as the titles for the GC look really childish for me (Super Monkey balls, Luigis Mansion, Pikmin...and the list goes on)....
the only game that I would consider getting with a GC right now is Rogue Leader and being that I hate games like that (flying sims type) then that game is eve nout of the question.
PS2 has been out a little longer and is a little older, but has a much better library, there has been time to work most of the bugs out with it, and to me represents a more well rounded solution, with the Game Cube being geared more towards the younger crowd (13 and under).
Now Personally I went with the xbox, but that is because I liked oddworld and DOA3, the upcomming roadmap for games looks decent, and it is a newer console produced by one of the largest companies in the world, so part of me feels that no matter what is said now the system will definately have a future.
Least if MS wants it to.