My view of the mid-mount through the gears v wheel motor
Running the motor through the gears allows you to use lower gear and higher motor rpm's in relation to a hub motor for climbing hills, this results in greater efficiency and less heat created.
Gear can be selected for best efficiency.
The centrally mounted motor gives far better weight distribution.
Lower wheel inertia meens the brakes will be better.
The ability to coast, only better than using a dd hub motor.
Drastically lower unsprung mass of the rear wheel, when used on a full suspension frame this is a huge bonus in suspension performance.
Slightly higher electrical consumption when cruising due to extra mechanical losses in the drive train.
More complex system that will require more maintainence/parts replacement.
Extra complexity could result in worse reliability.
Makes a little more noise than a DD hub.
I have owned both and would say the midmount is far better than a wheel mounted hub motor, but then that is my opinion based on the way i like to ride and the terain i ride on. For a person using their bike as a pure commuter the priorities could be quite different and a hub motor in the wheel could be the favourite.
On ES you fill find fans of both setups, we each respect each others point of view and accept that there is not a single option that is "best" for everyone so look at what you want to do with the bike and build it suit your needs and remember that the pro's and cons above are just my opinion and i am a mid-mount fan.
That makes me feel like we should all sit in a circle, when its my turn i will stand up and say, Hello, my name is Simon and i'm a mid-mount fan!