I give Princess Purina Tiny T-Bonz or pieces of Beggin' Strips for either a potty treat or to reinforce a behavior. I also buy Sweet Potato Fries & give those once in a while as well (she only like them on occasion).
For training I buy Beggin' Strips in bulk (way cheaper)...but they are way too much in whole for a yorkie. I cut it into about 10 pieces & sometimes even break those pieces in half, depending on how much work we're doing. This is her favorite treat ever, I think she would prefer it to chicken,
but again, it's not the most healthy.
The trick with Princess is the treats have to be moist, anything crunchy or cracker-like is just a waste, maybe your pup is partial to a specific texture, etc. as well?