I'm trying to make a computer that will use either 12.04 or 10.04 to host a Virtual Windows 7 machine for Cryptocurrency wallets.
Why so complicated? Why wouldn't you just install the wallets in Ubuntu?
Basically, should I use 12.04 or 10.04 for this? I'm thinking 10.04 because it is less resource hungry.
Software for 12.04 is more up-to-date, so I'd choose that one.
If the CPU is slow and/or old, the paravirtualization is going to be a much bigger problem than the GUI. In any case, you could install GNOME Fallback (sudo apt-get install gnome-session-fallback) if you don't want to waste resources on Unity or install a lighter distro (Xubuntu, Lubuntu, Mint Cinnamon/MATE), like maaku suggested.