I really liked Gnome 2, but I did not care for the attempt to re-make Gnome 2 as Mate. I don't really like Gnome 3. When Gnome 3 came out, I switched to XFCE.
However, XFCE felt kinda like a step backwards. So I tried Unity, and I liked it for a while, but I'm not a fan of some recent changes. Right now I'm using KDE 4.10 (or 4.11? I forget), and it is pretty slick. I installed a Unity-like launcher as well. I also installed XFCE's terminal emulator, because I don't like Konsole.
I wouldn't say any of these things are "best". What is "best" for you depends on how you like to use your computer, really. The nice thing about Open Source is that you can try them all and decide what you like, or even mix and match pieces like I did.