Several forum members have electrified trikes, some have used hub-motors and some crank-drives. I wouldn't say that one is better than the other. Like with bicycles, it's a matter of finding a system that meets your needs. If you want the motor just to help climbing, I'd choose a hub-motor. If you want help for climbing and at max speed, then a crank-drive. If you just want help to boost your high speed, then a hub-motor.
Sometimes, the design of the trike limits what you can do. If you don't already have the trike, before committing to buy, you should show it here, so that we can check the possibilities.