Mice vs rats, it's pretty much all the same gram per gram.
Yes there is a nutritional difference however there has never been a study on BP's nutritional's requirements.

What it boils down to is to feed what works and what is concubines for you.

Obviously most people feed rats because they get bigger and it eliminates the need down the road to feed multiple mice, which not all BP we accept mutilple preys and can also get costly.

So feed what works for you.

Now as far a prey size know that mice fuzzy are to small for any BP.

For an equivalence to feed your animals.

Smallest BP can eat a small adult mouse or fuzzy rat
The secon snake can eat an adult mouse or rat pup
The third one is fine on small rat.

Just remember the size of the feeders can vary greatly within the same range do just know that you should feed a prey equal your animal's girth size since those are hatchling and juvy snakes