As I recall, the motors are pretty similar. The torque comes from the Amps (via the controller), but of course your motor has to be able to handle the power and load without overheating.

Generally I think EM3 and MAC are going to be your most reliable solution, just be aware of the screw on cassette. Plenty of people use BMP motors with no problem, but those Asian vendors, with the exception of EM3, are not very helpful with support.

Here is an article on MAC and comparison to BMC if you want the long answer:
http://www.electricbike.com/bmc-hub-motor-review/

(that is a good site to poke around on).