I have a NExT in both hands. It is really depends on your use case. I mainly use mine for access control. Unfortunately the building I work in has some readers in strange locations, where it is easier to use my other hand rather than twist myself up in knots to get a read.
I suggest non dominant hand if you can, as it has less chance of accidental bumping etc.
I also have the xMagic gen2 and would recommend it over the NExT if you are going the access control route. It is easily programmed on the HF side with a phone and can be changed on the go. My work uses LF, and I program the HF for motels etc when I am away.