I use water softener salt pellets. I had pretty consistent deer coming into them, with some elk and the odd moose. I switched to the trace mineral salt blocks (brown ones) a couple years back and it really seemed to draw the moose in, and they haven't stopped coming. Most of my sites are there for whitetail, and the WT numbers seem to have really dropped since the moose starting coming regularly. The moose will lay down right on the salt for hours on end.
Edit to say, I only put the brown blocks out for 1 year, but even since switching back to pellets the moose are there consistently. They've almost become a nuisance.