I actually do think that an XBox 360 is better, I have played both, and I own an XBox 360 (I shall not be biased)
There are a number of pros and cons for each console, no matter how you look at it..
For example, PS3's have free online play, but for XBox, you'll have to pay quite a large sum of money to get Live. In my opinion though, with XBox, you're paying for what you get though, more money you spend, more you'll get.
With XBox, you'll get a number of games that havn't actually been released onto PS3 (yet) for example Halo 3, as far as I know, PS3 doesn't have that game, it's a pretty good game in my opinion, I prefer CoD4, but it's good if you like Si-Fi sort of games, which sometimes, I do.
I like both, they are both good consoles I suppose, it's just for me, the XBox is the one. It's more popular, it's not all that expensive, games are good, graphics are great, almost all games that are on PS3 + more.
PS3 though... Still a great console.