If the choice is between the two the question comes down to "Do you have friends?"
If you do, you probably want the 360. Xbox Live makes for a nice multiplayer experience. Playstation makes everyone roll their own multiplayer so it's hit or miss depending on the title. Netflix implementation is pretty slick and works well.
If you have bluray disks, then you might want the playstation. Tons of horsepower, but it's hard to harness for developers yet. When it's good, it's incredible. Current netflix implementation is horrid, ugly, chunky. Hopefully they'll fix it but I doubt it. The 360 example was too good to ignore, but they did.
Otherwise see what games you like and where most of them are. It's nice to have choice, but sometimes its confusing.