are you asking NEW machines or used?
as if used, honestly it comes down to condition and how it was used or abused more than I think model, as long as other things are the same!
and then the basic's would also apply,. what is the machine going to be used for, as some models have wider longer wheel bases, or some have 2 speeds, , or higher flow rates,and so on
so used?? condition matters most, if they have the same features one wants!
NEW
I think I also would like to try a side door model, like the JCB tele boom, seems like a great option to have
only flaw i see with them is, your always working from one side of the machine over being placed in the center, will take a little getting used too I would think, but not a huge deal!