I personally use a 64-bit host, but run 32-bit guests. I find it simpler, after a test, to wipe a VM and restore clean, and I'll occasionally update tools in my VM master images to test, snapshot etc. Just find it makes life easier, and removes most of the compatibility issues.
~ hayabusa ~
"All men can see these tactics whereby I conquer,
but what none can see is the strategy out of which victory is evolved."
- Sun Tzu, 'The Art of War'
OSCE, OSCP (Former - GPEN, C|EH - both expiring / expired)