Since you would only have flat terrain, a front hubmotor would be much simpler to install, depending on the front fork you have. If you have a lot of slick terrain (mud, wet leaves, etc) then the front motor will take more care to ride with, as you'll have to ensure you have sufficient tire grip to prevent losing traction, or reduce power on slicker areas especially when not going straight ahead, so you don't have the wheel slide out from under you.
It also wouldn't be hard on the IGH, sprockets, chainrings, or chain like a high-power middrive can be.
If you're planning on pedalling without assist a fair bit, I recommend a geared hub with internal clutch/freewheel rather than a direct-drive (DD) hubmotor, as it makes that a bit easier with less drag from the unpowered motor. But you can also simply use just a *tiny* bit of motor power to overcome the drag of a DD hubmotor if necessary. (with some controllers, like the Phaserunner, there's even a direct option for this in setup).
If a bit of drag (it's not much at typical pedal speeds, but it can be noticeable) isn't a big deal, then a DD hubmotor is simpler and has less to go wrong.
Either kind of hubmotor has less to go wrong than a middrive, and it also means you have effective 2WD, for redundancy if nothing else.