It would depend on the proposed owner and what they are looking for. If they are looking for an established business or one that's simple to start up following a set procedure, and to be associated with a recognised brand, then purchasing a franchise business would be the way to go to get working asap.

However if you'd like to generate a unique product or service and have the time, energy, motivation and some basic knowledge to start your own business, then starting a new business from scratch may be more rewarding.

As Deb said it depends on the owner.
A turn-key business might be had by purchasing the franchise but there will be still a lot of work in getting up to speed with the systems.
Your own startup may work just as well by modelling what is best practice initially and then listening to and evolving your business around your particular client base.