I am running both trying to decide which I will use to replace Windows. To me, unquestionably, these are the top two. I think I must have played with a dozen others. No winner yet. I think my choice will be driven by which has the worst/most problems. I have convinced myself either can do the job except for the bugs. Right now I am having a printer problem with PCLOS. I think there is a bug setting up third party drivers but no response on the forums. Mint broke the scanner use with Feisty (Ubuntus fault). There is a work around but that has issues too. Great... Printer or Scanner, choose.
Other than that, I find no real preference between KDE and Gnome. I do like Mint using Ubuntu repositories and the ease of installing almost any deb. If I had to choose today,it would be Mint.
Another fear I have is that when I pick one, what if the Zenmaster, Clem or Texstar, says no more. I have not evaluated the impact of switching distros. This may be my most important factor.
Actually, in spite of the fact I really, really want to replace Windows, the winner may be........arghhhhh! I can keep all this going because I have set up my configurations to share and synchronize all the data files I have so I can just flip back and forth.