There's a fair choice. If your workshop floor is nice and flat you may get away with having 4 castors and brakes, whether all the castors are swivel or only 2 swivel is down to personal preference. I have both types and they each have their advantages depending on what your moving and the space your moving it into. Are you looking to be able to move something 360 degree whilst remaining on a fixed spot?
However, my preference is for one with 2 fixed castors, 2 swivel castors and then 2 wind down feet. This allows any floor undulations to be taken out and the stand is rock solid with the feet down. I have the Axminster light mobile bases and they're good but expensive when compared to other makes from the likes of, Charnwood, Rutlands, Yandles etc, I can't speak for they're quality but I'm sure someone on here can.