I use a collar. Works better for me, as I use the harness for actual assistance stuff. He's trained to NOT PULL on the collar, and DO PULL on the harness. I only prefer harnesses on tiny dogs, and even then if you ever want to compete in obedience or rally with them they MUST be in a collar, NOT a harness.
So, somewhere down the road would you like to dabble in obedience or rally? Then the dog will need to wear a collar.
I almost always say command. Cue, to me, is more the actual movement or word I associate with the command, and the command is what I actually want the dog to do. Maybe that's just me, though.