I've done some asking around, and right now I'd say I'm leaning towards X-box.
To be honest, I haven't really looked at GC because I've never been much of a Nintendo fan. The Nintendo exclusive games they put out on past systems, like Mario, Starfox, etc., are more geared towards kids than adults... no offense to anybody who likes those titles, but those kinds of games just aren't my taste. I assume this trend is cont'd on GC.
Another reason I'm thinking X-box is because, unless I'm wrong, it's got the most power (better CPU, more RAM) than the others, and better graphics, gameplay, I'd assume. Not having to buy a memory card is nice too. The major knock I hear about X-box is that there's less selection of games compared to PS2, but that it's getting better.
Thanks for the feedback so far, and if anybody has more to add I'd appreciate it.