Gram per gram it's all the same, while there is a difference between mice and rats when it comes to nutritional value, there is no study on the nutritional requirements of snakes.

It all comes down to feeding what works for the snake and is convenient for the owner.

I have snakes that eat mice exclusively, some that eat rats exclusively, some that eat ASF exclusively and some that eat anything I throw in there, and all are thriving regardless of their diet.