Well, your game category leanings seem to point more in the direction of the X-Box. It seems to be the stronger FPS and \'espionage\' game system.
For Gamecube, you would probably want to check out Metroid, which is a great FPS type game, and better than Halo in my personal opinion. There are a lot of great games for GC in other genres than those you listed, and I think it is the stronger console overall, but if you really wanna stick to the three types you listed though, X-Box is probably the smarter choice. That is the direction they are leaning in, and focusing on.
By the way, when you read this, take in mind that I am, if anything, a Nintendo fanboy.