I know that about six billion people have compared and contrasted the differences between the Ubuntu variants. Really, the choice comes down to personal preference, and usually it comes down to the classic Gnome vs KDE war. For years, I avoided X11 altogether, because most of the work I did was in the terminal, but even old CLI guys like me can see that a GUI is really a requirement in today's tech world.
For the record, since it's been available, I've usually used straight up Ubuntu. With all the stories recently on the Linux Journal website, however, I felt the urge to try KDE, in the form of Kubuntu. While I'm sure it will offend half the people reading, I have to admit that I really don't like Kubuntu. And the cliche, "it's not you it's me" rule applies here as well. KDE is great, but it's just not great for me. I really tried to like it, I mean, I read that Linus himself is a KDE user. I think the reason it turns me off is that I don't like the mainline applications. I don't like Konqueror, Dophin, Kmail, Kaffeine, Amarok, or even Kterminal. So for my daily use, I end up doing my best to avoid all the applications that are so tightly (and well) integrated into the system. And artsd? Ick. (I guess KDE4 will help with that, but still.)
Gnome is better (again, for me -- no flame wars now...), but it seems bloated. I can't really say why, but it just feels sluggish. I can't seem to configure it the way I prefer either. The gconf stuff is just complicated, and honestly, reminds me of the Windows registry thing. I do like the Gnome apps better, but even with that, I don't use Evolution. It's too much like Outlook, which I really really don't like. :)
So what's a lazy user to do? Well, you could try NotYourBuntu -- but that only works for me (and then, only in my imagination). ;) If you're really not happy with Gnome or KDE, however, Xubuntu offers a really nice alternative wrapped around the XFCE desktop. It's fast, light, and doesn't get in the way. I don't feel as tied to specific applications, and mix & matching my favorites from the Gnome and KDE lineups seems to work very well. Since my application preferences vary widely, that's really important to me.
Xubuntu might not be for everyone, but if KDE doesn't light your fire, and Gnome seems like it uses more resources than you can spare -- I'd suggest giving XFCE a try. The Xubuntu installer works just like the other *buntu flavors, and it's everything I've ever wanted in a distro. Give it a try, you might like it.
And if you don't? Well, that's what's great about Linux. If you don't like it, you don't have to use it. It's all about choice.
When it comes down to it, I love Linux any way it's sliced. Picking one distro or desktop manager over another is a lot like picking a favorite ice cream. Even the flavor you like the least is still ice cream!