All 3 version are easy to use. If you have a reasonably powerful computer I'd recommend the standard version with the GNOME desktop. If you are running older hardware I'd go for the XFCE version. The XFCE version is still fully functional, but it uses less resources and runs faster (although GNOME looks nicer).
KDE is the most resource hungry, and to me doesn't offer anything that GNOME doesn't, and I find GNOME more intuitive and easier to learn. That's personal opinion, though.
You could just install one version, then install the other desktops and try each one. You choose a different session at log-in to change desktops. All 3 versions are very nice and you really can't go wrong with any of them.