You've got a 360, right? I'm pretty sure the first four games are backward-compatible now. I would get the Xbox versions of all of them. The only possible exception is Double Agent, which actually has a 360 version. The difference is that the original-Xbox version has a splitscreen or online coop campaign, while the 360 one has extra multiplayer modes.
If you still want to choose between Gamecube or PS2, it depends on your priorities. I don't think any of the PS2 games have splitscreen, and the graphics are absolutely horrible compared to the other two versions, and levels are much smaller, but it does have online. The Gamecube versions have everything the same as on Xbox, including splitscreen in Chaos Theory and Double Agent, but no online modes.
It's also worth noting that there's a Wii version of Double Agent, though I can't speak to the quality of that one as I haven't tried it.







