My mobile bases slide on low-friction, ultrahigh molecular weight (UHMW) polyethylene pads. Fastened to these sliding bases, my tools glide easily over the concrete floors in my shop, yet there's enough resistance to keep them stationary during use. The bases are compact, so I don't whack my toes on them, and I don't have to worry about forgetting to lock or unlock casters.
Each sliding base costs about $20 to make, much less than a caster-equipped mobile base. The pads (see photo) cost only about $2 apiece, because they're cut from a 3/4" thick sheet of UHMW polyethylene (UHMW polyethylene sheets are avaiable from Lee Valley Tools, www.leevalley.com, ).
I've found that a push-pull method keeps top-heavy tools, like my drill press, stable. I push lightly with my top hand to keep the tool from tipping forward and pull with my bottom hand to slide it.