For several reasons, I have I would prefer to use VMware. At any given time one might have better features that the other, but wait a few months and the other one will be better. It also seems like Parallels doe supgrades more often just to suck more money from people whereas VMware adds some improvements in patch updates. Also the fact the VMware works without work arounds in Mavericks says something good about the application in my opinion.
I personally prefer VMWare, feels like a more robust product to me. Also, VMWare Fusion 4 (not even 5!) seem to be working fine on my Mavericks installation, although I cannot say that I've tested it thoroughly yet.