Best Bench levelers I have found are hockey pucks.
These chunks of rubber are about 91 Durometer on the Shore A scale so they do not have much give.
Before I installed them on the workbench it used to slide on the concrete floor whenever I was pushing on the bench the wrong way. With the hockey pucks under there, no more movement, no matter how hard I wail on something. The 9x28 Logan lathe I could drag across the concrete floor no problem, after putting on hockey pucks, needed help to lift and move around as it almost felt like it was suction cupped to the floor.
Pucks are 3" diameter and distrubute the weight really well.
To make the parts needed:
Drill through 1/2" diameter and counterbore 1-1/8" diam x 3/8" deep.
Cut a washer from 1/4" plate. I use a 3-1/4" diameter holesaw, then drill the pilot hole out to 1/2", mount on a mandrel and clean up the outside on the lathe.
To Assemble:
Take 1/2" carriage bolt about 3" long, hockey puck, 1/4" plate washer, regular flat washer, split lock washer and nut. Tighten. use one or two more nuts as jacks and locks as needed.
If I need to move the machines or tool boxes around then I use the Footmaster Castors. They have a built in levelling foot and a machine can be positioned and levelled very quickly with them. Footmaster is the company that made the first levelling castor and are manufactured in Korea, there have been a few companies that have copied them as the patents have expired, or just plain pirated the idea.
http://www.footmastercasters.com/
Walter