At this point, either could be good.
360 came out earlier, has a large amount of game titles. It also has the great online feature which is its biggest draw. Plus many sony-only titles have switched over to both platforms due to the PS3 taking so long to come out.
So, lots of titles, great online play, pretty stable now. Good price.
The PS3 finally has come out and is doing well, after being released late and at a high cost. Prices are decent now, though cutbacks have been done to the system to compensate. Many new titles are starting to appear, the prime choices for the PS players (grand theft auto, MGS, gran turismo, etc). It also has great dvd function with blu-ray and upscaling. Not good online. Not a huge selection of titles, but this summer with have MANY new ones.
Personally you can't go wrong with the 360. It has more games than the PS3, it has MOST games that used to be only for the sony (such as GTA4), many console restricted games are for both now. It has online play which kicks PS3 out of the water period. So, cheaper, more games, most same games as the PS3, online play, it is superior in most catagories.
The only reason I would say to buy the PS3 over the 360 is if you plan on taking into account the dvd blu-ray function of the PS3. If you watch alot of dvds, and have a good system set up for it, the PS3 will function both as a play console and a good dvd blu-ray player, saving you the cost of actually buying a blu-ray player or upscaling dvd player.
So its up to you, what do you use it for. Id go with the 360 myself even though I'm a sony fan. Maybe in another year it will be better, but as it is now, even the games comming out for the PS3 that were sony-only are BETTER on the 360. Take the new grand theft auto 4, which EVERYONE is waiting for. Its the same for both systems, but the 360 has MORE content, because of the online play, you can play with friends, you can download 360 only special modules and new content which the developers are producting. So not only do you get the same game, you get MORE content simply because you have a 360. Same with many other ex-sony-only games.
The 360 is better in every catagory except the blu-ray player, soooo you figure it out.