Like the author, I also tried to upgrade from 12.04 to 14.04. The difference is I was on a desktop VM. I went with just upgrading the existing VM thinking it would take less work than spinning up a new VM and transferring all my files and settings, but that turned out to be a huge miscalculation.

Originally left it to upgrade overnight, only to come in the morning (this is on my work machine) to see that it hanged somewhere in the process and wouldn't move on without user input. So I proceeded with clicking through all the prompts, and when 14.04 first loads, it's SO SLOW. Long story short, it took me 4-6 hours to finally get it usable. The whole time I was thinking, "how could they mess this up so badly?"

The host OS for the VM is Windows 7, and I have to agree with the author, it is much better to use. I only run the VM for the command line, but may upgrade to Windows 10 when Ubuntu on Linux comes out of beta this summer.