X-Box has a more gamer "fair" online play system. PS has a more developer "fair" online play system. I will explain...
XBox you pay $50 a year for online service, and any online playable game available for XBox is then fair game for you to play online. PS is a different story altogether. Sony provides no servers to development teams, so if a company wants to make it's game online playable, it has to set up its own servers. Thus the gamer pays a variable monthly cost for each game that they want to play online on PS. The result, is if you'd like to play a number of games online, which most gamers tend to want, the XBox system is cheaper and more consistent in online experience.
