It all depends on your gearing, ESC, and hop ups. If your car is totally stock, you'll never handle a 10T.

Best motor all depends on what you're using the car for. Since you posted in the RC drift forum, I'm assuming that you only want to drift your car. If that's the case, you'll want a motor from 15T all the way up to 35T. Most drifters use 27T pro stocks, 19T spec motors, or brushless motors.

As a precaution, I would recommend you getting the aluminum driveshaft, metal motor mount, ball bearings, motor heatsink, spare spur and pinion gears, and even a better ESC. Also, you may want to upgrade the shocks to oil shocks like the Tamiya Mini CVA shocks, or the TRF shocks. You might also be interested in the aluminum steering set to remove steering swap, and front universals to get more accurate steering.