The best motor(s) is(are) the one(two) that:
- leave(s) you enough weight budget for the rest of the chassis, batteries, and electronics
- has the appropriate gearing for your application
- has the strongest torque given the input voltage you supply
- has the best durability record
- you can afford
You need to look around for various options from various vendors, and do some calculations on the other weights involved, as well as desired wheels and traction options, before you can narrow down to a particular motor.