Not the parent, but anecdotally, Vagrant + Parallels runs MUCH faster on my 15" MacBook Pro than Vagrant + VirtualBox. VM startup time is shorter, and CPU usage seems to be lighter. For instance, I worked on a project where I had a long-running process that would do a lot of file I/O and periodically collect the results and run some calculations. On VirtualBox, this basically pegged a CPU core while it was running, but when I switched to Parallels, CPU usage hovered around 5%. (I'm guessing this particular example is more to do with VirtualBox's dog-slow shared folders, but still relevant, I think.)
