Many trainers, myself included, will ask you to rank your motivators. We do this because we want to be able to strategically pair the value of the motivator with specific circumstances in training. The basic idea is that more difficult work or effort would be paired with higher value motivators, and vice versa.
The problem with this is that while it works reasonably well within a type of motivator (preferences for a specific type of food, type of toy or approach to personal play) it doesn’t work nearly as well if you switch types of motivators.
Brito prefers cookies to toys, in the sense that if I made both available, he would opt for a cookie. But in terms of his energy (caused by knowing he is about to chase a ball), his focus, and his endurance, I’d say the ball gives me a better overall result for practicing known movement-based exercises. I cannot compare food to toys because the entire effect is simply different.
Lyra and Raika always prefer a toy, no matter what type of food I might have available, but I still use food in their training, depending on what I am trying to accomplish.
Some dogs clearly prefer one to the other and their preference is expressed across the board, but plenty of other dogs are not obvious; their preferences might be a function of their environment (food might work where a toy might not), the work under consideration (heeling might benefit from a toy whereas a recall might look better with a cookie), or something else altogether, like time of day, the specific cookie (or toy), how hungry the dog is at that time, etc.
So which is preferred?
There is no real answer, and at the end of the day, it’s not important. What is important is understanding what motivators are most effective, for a given dog, under a given circumstance. Once you have a handle on that, choose the motivator that is going to give you the attitude, energy, and clearness of thinking that makes sense for whatever you are working on.
When considering motivators, think in terms of “appropriate for the circumstance”.