The only mowers I have experience with are the New Holland 450/451 (3pt) and equivalent trailer type (model 455 I think). For this size tractor the trailer type are going to be the easiest to setup/hook up, provided you have a hydraulic remote valve on the tractor. Just drop in the hitch pin, hook up the PTO shaft and hydraulics and you are ready to mow.
I have a 451 model which is 3pt hitch type. To use it on a B-series Kubota you need the optional toplink adapter for compact tractors. I made my own and it was fairly straight forward if you have welding capabilities. The 3pt hitch mower is more compact and maneuverable, but also harder to hook up. I was worried about the weight, but my B3200 handles it fine, even on moderate slopes. If you get on a steep slope with the mower on the down hill side, you have to be careful, but for all of my uses (mowing hay, around the ponds, etc) it works fine.
I don't have any experience with one, but one of our neighbors used a Ford 501 sicklebar mower on a B-series Kubota, seemed to work fine as well (but is not belt drive.) Regardless, stick to a maximum of 7' cut or less, the 9' mowers are way to much for this size tractor.
Attached are a couple pics of my tractor with mower (mowed about 15ac of hay with it that day.)