This year we did six wheel drive with a unique twist. We originally tried four wheel drive, but wanted a tighter turning radius.
We didn't like the tippy drive with the center wheel lowered so we used omni wheels on the front and back with all wheels at the same height.
On the kitbot frame we drove the middle and back wheels with the toughbox gearboxes. Then we slaved the front wheels to the middle ones (so the middle wheels had two sprockets - one on each side.)
Picture:
6WD Pic
We were happy with the results and seemed to have quite a bit of power.