>>1
What
>>3 said. Especially:
>it won't make a difference until you know what you're doing.
To which I would add: "And once you know what you're doing, the difference won't matter."
People treat it like a huge, life-alter decision, but the irony is that, by the time you are moderately adept at using *nix, you will learn to HATE BOTH KDE AND GNOME. Desktop environments exist to hold your hand. That's fine for what it's worth, but once you learn to fend for yourself, they are big, bloated monsters that just get in your way. Eventually you will probably find yourself looking for something lighter-weight.
So just pick one based on what catches your eye in screenshots, and use it until you tire of it, then find something else.