Mice are great, cheap, tasty, and good for them. Rats have much higher protein, and more meat on them. They tens to be the better choice for feeding snakes I know. Rabbits are great for ferrets. I know there is a nutrition sheet with the different feeders, rodent and insect, somewhere. I posted on my reptile forum asking about it as that is where I have seen it multiple times. I will post it here when I find it.
There is no one protein source that covers all that needs to be covered. That is why we advocate the feeding of multiple protein sources (minimum of 3). This way you're covering as many of the trace nutrients needed as possible. Supplementing is no different than what they do with kibbles, it for the most part does not cover the nutritional gaps that are left by feeding only one protein source. In this age of easily accessed varieties of protein there is no possible reason why someone should find themselves feeding only one protein. So in answer to what I'm understanding of your question....there is no ultimate, sole source of protein. ciao