Get the largest one you can afford. I started with a 6x10 and ran out of room so fast. Now have a 7x14 and still think I should've gone with the 16 footer. Either way I still think that if you can scrounge up more money for the larger you'll be happier. Then if you ever need to haul a larger piece of equipment it will fit. Also my 6x10 could get about 5-6 yards of mulch with side boards. 14 ft has done 10 with room for more. Also on large landscape maintenance jobs the trimmings and edgings would fill that 10 footer to the edge. 14ft has also enabled me to carry different materials at once with easy loading for the skid steer driver at the nursery or loading yard. I created a divider to have two 7ft sections.
Scissor lifts are better but the dual cylinders are fine. My 14 ft only came with the scissor lift or single cylinder at the front which according to my manufactuer (Sure-Trac) is the strongest.
Then there is power up/power down or power up/gravity down. Both of mine have been gravity down and I like that the going down is much quicker and doesn't use the battery to do so. Also if the batter should die the body will still come down with gravity down.
Get EVERYTHING. Multi function gate, ramps, adjustable coupler, etc...
There are also drop axle vs straight axle. Drop axle is easier equipment loading whereas I went with the straight axle to easily load my wheelbarrows with mulch/stone/topsoil. There are deck overs too that are much higher for easier "pile" dumping and wheelbarrow loading but not so equipment friendly. Some deck overs have drop down sides for pallet loading. I almost bit on a 14ft deck over with drop down sides but the price was about $2k more than the one I picked up!!
Again I'd rather be "Wow I have a lot of space leftover" vs. needing to make 2trips. Just my thoughts.
As a side note my 14footer was a 14k GVWR with a 10,400lb capacity. I had to have the factory send me a derated label to 13,200 because with my dually I would have been over 26k combinded needing a CDL which I do not possess. Again I have a new certification label not a registration adjustment.
Good luck in the search!