Thanks so much for that link TobyMac! Great information. I thing I will get 2 of the large motors. That way he can have some power, and if there is a need for 2 matching motors, he can have that. Also, since the large motor is not much bigger than the M motor, it will be easy to integrate into MOCs.
I want to order a couple power function motors for my son. He has the Lego City 7939 Cargo Train, which is a great set, but the train motor has its limitations when it comes to versatility. I want to get him 2 power functions motors to use in his MOCs. What are the 2 most useful power function motors to have? From what I understand the smaller motors are faster, but less power. I was thinking a medium and an XL, buy maybe 2 large would be better... Suggestions please! Thanks!