It probably doesn't matter much which Linux you install on a desktop. The user experience will be determined by Gnome or KDE, not the distro.
The two aspects of linux that have the biggest user-experience impact are the desktop and the package system. Linux has, sadly, two of each.1.
There are two desktops: Gnome and KDE. In general, you can choose Gnome or KDE with any distro and you can even install both. (You only run one at a time, though.) Please realize that except for some configuration details, for the most part the distros redistribute the same set of Unix-model software, so you aren't getting anything wildly different or even as different as XP vs Vista.
Either of the two main package systems can in some ways be used with any distro, but life will be much easier if you stay with the vanilla one for your distro. But since you aren't expecting either one I think it won't matter.
Now, if you went and installed, say, NetBSD, then you might notice some real differences, although you would still have your choice of Gnome or KDE.
1. Technically, there are 10 or 20 window managers that provide interesting lightweight GUI's that are something a bit less than a full-blown desktop GUI, but that's in the advanced class. Also in that class: Unix servers generally run no GUI at all.