I prefer back fat as well. I've had good bison suet, but in the order I put in through Northstar a few of the packages of bison suet were good and most were hard and dry like cattle suet.
On another note, if you want very high quality fat you might consider getting in touch with a local game processor. They generally cut the back fat off deer, elk, moose and other wild grazers and just throw it away, as hunters never want it. I asked a local processor if he'd save me the back fat from the deer and moose he processes, and he said sure. I drove out for the first pick-up earlier today, and returned home with about 100 pounds of clean back fat from wild whitetail deer and a few moose. I tasted some and it was far, far better than any cow or commercially raised bison fat I've ever had, whether back fat, suet or marrow. And this is just after the first two weeks of the season; we have another 2 months of hunting season left so there's much more prime back fat where this first load came from.
