I know this thread has been dead for a bit... but I wanted to put in my 2 cents:
It's more than just what you like... it also depends on what you intend to use the machine for. Personally, I dual boot windows and ubuntu because I am a programmer and they both have great tools. If you're running a server you'd want xubuntu because it'll take up less resources from the system. Like Washe said, it's a tactic by ubuntu to get more of a user base (they are after all a business of sorts).