While looking try to find a brand that fits your tractor! Don't look for one that can pickup more then the factory unit, I think Kubota knows more about the tractor then a loader company might!
The bulk of loader companies get to make more money from a design if it fits more models and makes, see if you can see one on a tractor. Some companies will even use egg shaped holes so they can fit more makes and models, stay away! The loader itself will try and make the holes bigger if they get loose! Don't start with one!