I'm a walking liver treat!
I work with dogs day in, day out. Everything I wear seems to end up with liver treats in the pockets, they go through my wash, my dryer, you name it, when I pull coins out of my pocket, drive my car, look through my handbag, there are always crumbs or actualy pieces of liver treats!
Liver treats I find to be the best for training our dogs, they are low in fat and low in salt and MOST dogs love them...only a couple of extra fussy ones won't, and thats when I'll use tiny dried fish pieces OR chicken but only if i have to.
Liver treats are easy to break up and treat your dog without having to give them big pieces when they've earnt them. They are great to scatter around the garden too, keep your dog focused on finding treats all throughout the yard and its fun and keeps them interested in that instead of you leaving your house for instance!
Make sure your treats for your dog and low in preservatives, fat and salt and you will be rewarding your dog in a healthy way.
Eventually you want to wean your dog off treats for learning too, they need to listen to you and respect you rather than just doing what you ask for a treat and nothing else.