I have the host OSX for administrative tasks
and then one VM per Windows OS.
I would prefer to have one VM per customer but have not come around to it.
Setting up a new VM does not take that much time but installing Visual studio, Sqlserver, Chocolatey and configuring everything does. When Windows updates 7->8->8.1->10 I create new machine and copy stuff I need as I go; instead of updating the VM. This is my way of continuously cleaning my work space.
The only issue I have run into is multi monitor support that sometimes is a bit shaky to set up but it has stabilised every time. (as I write this my second monitor switches to green every time my screen saver has kicked in and I have to replug it)
I run Parallels which is not gratis and not even cheap. To add insult to injury they make sure to not support newer OSX and Windows versions as they come out. This means that the one time price (presently upgrade is 50€) has to be paid several times, like every other year or so.
I have not compared Parallels to their competitors Fusion and Virtualbox. AFAIK Fusion is about the same in both functionality and price. Virtualbox is free as in F/OSS.
The reason I started with Parallels instead of Virtualbox is twofold:
1) I was new to the host:OSX/vm:Win arena and wanted something someone said worked. (I did not want to buy a fancy pansy mac just to install windows on it)
2) By that time Virtualbox could not handle bootcamp.
My plan was to test to run Windows as a VM and if it wasn’t performant enough switch to bootcamp. Then I learned that to be able to run the vm as bootcamp it has to be configured as bootcamp to start with. I never did and I have never had the need.
(I would love to try to have the dev machine totally remote. Then I could have a phat machine without the fan noise.)