sign in to websites using your personal web address, without having to use your e-mail address.
What is the point of that? For convenience, email addresses are much easier to come by than is web hosting. For being securely anonymous it's also much easier to do through email — but not by so much that requiring a website rules it out, if that's the intention.
I've used them both in the past, but prefer Xfce now. So I'm probably not too biased either way on Gnome v. KDE. I'd say they're both extremely well-supported, popular, respectable, and safe choices. They're quite different in style though, so odds are you might find you have a preference for one or the other. Go with whichever you like best.