Advantages: Price weight length and ability to expand areas of camping Disadvantages Size/space lack of redundancy in case of a flat Carrying capacity (in some cases) I just bought an ...
The only reason I have a single axle is that they don't make a double axle in a really small trailer. Folks who have had both say that single axles are tougher to back up with -- more squirrelly.
To me, the very biggest disadvantage of a single axle is that in case of a blowout, the trailer will tip far from level and could tip over. At highway speed, this could be exciting.
So I would say that all other things being equal, get a double axle if you can.