I've spent a few years with both of them, and in the end, I dind't find them to be much different (from gnome 2 either), one has a cute mouse as a mascot.
They're both excellent and could be configured to fit my fancies.. In the end I probably preferred xfce for some reason I can't quite put a finger on..
3 years ago I switched to i3 and haven't considered switching again.. I still keep xfce around for a few specific uses that relates to running old computergames on WINE where it's more effort that I'm willing to put in to get them to work.