I wouldn't recommend getting either system simply just for Assassin's Creed (which I get in three days, YAAAAY!). It'll be out for the PC soon enough. Now, as for choosing which system to get in general, it's my "professional" hardcore gamer opinion that the PS3 is the better investment. Granted, I prefer RPGs and with the next FF and the next Suikoden both coming out on the PS3, and with PSs general reputation to be the RPG console, PS3 is the console for me. Alas, Assassin's Creed is really the first worthwhile game, in my opinion, to come out for the PS3. But, it IS just the first. FF, Suikoden, GTA, Resident Evil 5, and a few other promising games are well on their way.

If, on the otherhand, you're more into FPSs and an already established game library, 360 would probably be the best bet. And, of course, the cost is always a plus. But, keep in mind, that PS3s are now, or soon, being offered for $399, which is, if I recall correctly, about the same as a 360. Anyhow, XBox has always had a wider variety, IMO, of FPSs.

Now granted, I think in the long run, it may not really matter which console you get as more and more games become available simultaneously on all of the consoles.

What you shouldn't get, in my condescending gamer's opinion, is the Wii. It's cute, and kinda fun, but for a serious gamer, it doesn't hold much.

Anyhow, hope that helped! Regardless of your choice, it is somewhat of a investment, so be sure to do some research. :)