VirtualBox on the Mac is very nice. A respectably small download, an easy install, a pleasant GUI, it feels very polished and in my light use, both featureful and stable.
Basically they are all pretty similar, if you use it in a serious environment there are probably more tools and consultants that will tune Vmware server for you, but for ordinary use it's probably a wash.
I recently made the change from Macports to Ubuntu on VirtualBox. Things are much nicer now. My one tip would be to have any datafiles separate (ie not read/write files on the Mac filesystem directly - even though you can) and communicate between the two "machines" using version control.
I think this is the way to go for everyone newbie or not. If you're not going to be deploying on OS X then why develop under it. VirtualBox with your deployment system on Mac OS X gives you the best of all possible worlds.
(-: Please don't flame me. I might like ports as much as apt, if I knew it better. :-)