[Cory]

You might want to add Drills+CIM's.

As for your question, either one will prove to be fine. The Drills have a bit more power than the CIM's. They can be shifted using their transmission if you wish, and you already have the mounts and gearboxes if you dont want to make a chain and sprocket drive. People have voiced concerns with the integrity of the transmissions, but if you do it right, there wont be any problems. Also, the drills wont backdrive in their standard configuration, which may or may not be an advantage.

As to the CIM's, they are very easy to mount using the holes on the face. (10-24, I believe?) They still have a good amount of power, they don't overheat as often as the drills. They don't have an anti backdrive feature like the drills. They are also a bit heftier than the drills. One plus is that they spin at approximately the same speed forward and backward, unlike the drills, meaning that your robot wont drift to one side constantly.

Cory