Hub motors give you a really heavy rear wheel and a lot of unsprung weight.
Make sure the hub motor is going to fit your swingarm well before you buy it, but you'll need to make modifications either way.
Mid Drive Pros:
-Weight is sprung so leads to better handling characteristics
-No modification of the swingarm
-Easier to set your own gearing
Mid Drive Cons:
-Chain maintenance
-Takes up space that could be used for batteries and other components.
Hub Pros:
-Very space efficient
Hub cons:
-Heavy unsprung mass in the rear wheel gives worse handling characteristics.
I don't think mounting is a problem with either motor type, they just have different challenges. Oh a mid-drive you have to make sure your in the right spot and your alignment is good. You need to be accurate, but on a hub you're modifying the swingarm to both accept the motor and deal with the torque, and you're mounting a new disc brake. Either way you're fabricating, though depending on your comfort level one might feel more intimidating than the other. No matter which way you go I would get good measurements and have at least a rough mounting plan before ordering the motor.
I think at the end of the day the question is do you want your bike to handle better or have a bigger battery. These are the biggest tradeoffs.
If you haven't, check out endless sphere and elmoto.net, they're much more active forums for conversions. This community is mostly owners of production bikes.
