I use verbal aids very sparingly. I use them a little more on green horses but it is mostly "smooch", "easy" and "Ah!". [ "Ah!" stops about every horse, dog and person around here right in their tracks.]
"Whoa!" is never said here. Here, it means one thing and one thing only and that is 'stop hard and slide'. You will find that most reining trainers save "Whoa!" for sliding stops and never use it any other time and do not even use it for every stop.
I never want anyone to use "walk", "trot" or "canter" while here because any horse that may go to the show-ring is likely to 'cue' off of the announcer. Any horses I use for lessons will go one gait faster from a "smooch" (as will my horses on a longe line or in the round pen) and will drop down a gear with an "easy".
That's about it. I want them tuned in to my body language and my hand, leg and seat aids much more than my voice. Voice is not used in the show-ring (other than "Whoa!" for reiners) and is a distraction as far as I am concerned. Obviously, it is not necessary as there are a bunch of World Champion reining horses that are stone deaf. Voice must not be a requirement for any training if a deaf reiner can be a World Champion.