I've looked into things a bit as I'm setting a virtual game up too, my first one, and I just wanted to add that I've found that since my system has little memory running applications like Battlegrounds and MapTools was prolematic. OpenRPG run easier.
I've got no experience with how it runs in pratice, this was just trial runs to see how the program works. OpenRPG worked, but MapTools got hang up and barely functioned, as did Battlegrounds.
I've obviously chosen to go with OpenRPG (and Skype). I've decided free is a must, for the players' sake, and I like the fact that I can program OpenRPG, at least in theory, so can make dice and so on (I need special dice to run Ars Magica - stress and botch dice); now if I only knew how to program in Python...