I recommend experimenting with each profession briefly. You can switch without cost, but you lose skill progression. Some have a mini game or dialogues. Decide which you like better from your perspective as the player before worrying about demand of other players seeking your services.
As far as player demand for services, I am more likely to seek out a surgeon or sexologist or trainer that will permanently enhance my actors. I believe most of the beauty therapist bonuses were temporary? Demand for your services will also be impacted by the location of your clinic versus where the other players are active. You might find a lot of player demand for services even in a popular profession, depending on your location or inactivity of other players.