I started out with PS2. Because in the beginning, PS2 had the biggest library and backing for all my old PSX games. There was no reason to get an Xbox or GC. As of a month ago, I finally bought a GC. Why? Because the GC library finally had enough titles that I REALLY wanted to play. And the titles are what make the system. I said to myself, "damn the GC is pretty cheap and I really want to play metroid prime, zelda wind waker, sc2, fzero gx, eternal darkness". So I got it and got all those games with it. Almost every game on that list is an amazing title. So for a few hundred bucks, I got many many hours of entertainment.
See, what I do is I go to
www.ebgames.com and look through each of the sections. Then I add games to my wishlist that I think I may like. After adding them to my wishlist, I do searches on common game sites / google for good reviews of the games. If the reviews show that the game is just pretty colors with no real content, I then remove them from my list (most good reviews can give you a good idea of whether you will like a game or not). At this time, I havn't found enough games in my wishlist to bother buying an Xbox. I think it would be cool to have all 3 consoles, but it hasn't gotten to that "ok thats it, now I MUST buy one" point.
Crossplatform titles are another issue. At first, I only had the PS2 so I was only buying crossplatform titles for my ps2. But after using my GC, I realize that the hardware is truly superior to my PS2 and I would rather get crossplatform games for my GC. The thing is, my GC seems to load and save MUCH faster than my PS2. Loading / Saving is one of the most annoying things when it comes to a PS2. If I had an Xbox, I would probably buy most of my cross platform titles for it, because it has the most superior hardware. Except Soul Calibur 2, because Link owns .
Now, unless some amazing games come out for the Xbox in the near future, my next console will most likely be another PS2 to replace my aging, broken one with a void warranty. But if my PS2 was still in perfect condition, I would be buying an Xbox and finally have all 3 systems.
So, I suggest you do this. Go to ebgames.com and start a wishlist of all the games you would like to play, regardless of platform. Now go into that wishlist and rate (in your head) all the games by order of 'necessity'. Then count them up and see which console will give you more enjoyment. And then buy that one.
PS. If GTA/GTA Vice City or Halo are selling points for you, Make sure you realize that those games are all available on the PC now. Well, Halo will be this month.
I hope this long winded post helps you get a better idea of what you want to get.