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.
VMWare Fusion 5 works fine on Mavericks. But I am still a bit ticked off that there's no way to disable discrete (high performance) graphics in Fusion, which sucks battery life.
Parallels for sure. It has traditionally performed better than VMware Fusion and is compatible with Mavericks so long as you use the launch script on their knowledge base site.
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.