To be honest, I don't think your choice of DesktopEnvironment will make much of a difference either way. Your package management is going to pull any libraries needed anyways and the underlying stuff doesn't really change just because you chose Unity over another environment.

Depending on your PC, it might make sense to go with one of the lighter options to give that VM all the horsepower it needs. I have read comparisons where Unity turned out to be rather heavy on RAM compared to the competition. But since you and Unity obviously get along well and it was your intuitive choice, I'd say go with it and just slap that virtualized Windows in there. Chances are, sooner or later you'll be curious about other DEs or distros, anyways - especially if there's already a VM just waiting for tasty disk images.

Oh, in case you haven't installed it yet, I recommend you get a (Windows-)tool called Unetbootin and use an USB stick. As you may know, Ubuntu/Mint (and most modern distros) can boot from their installation medium without even touching your hdd, so you can test-drive in peace. That can also be quite handy in case you need to fix something - I usually have a distro on my keyring.

You do however also get the option to create some space for persistence on that stick, so you could effectively test over several days and keep your changes between reboots. If you manage to break anything important, just write a fresh installation to the stick... Nothing like simply booting into the real thing when it comes to finding the right flavor of Linux.