Cornsnakes have been known to eat just about anything with fur...This includes but not limmited to hamsters, mice,rats,gerbils,guinea pigs,rabbits...As long as the food itm is not to large...They also can and will eat chickens,quail,ducks, other birds, bird eggs, anoles, salamanders,skinks, worms? and even other cornsnakes...
Nutrition wise these animals will vary depending on size and stage of growth and type...Ex. a fuzzy mouse is more nutritonal then a pink mouse because they have a more solid bone structure, which provides more calcium for the predator...It all boils down to what you feed the prey animal and how healthy that animal is...I have believe rats and birds to be more nutritional then mice and lizards but that's just my preference...
The disadvantage's of certain prey items are the cost and the fact that the snake may become "addicted" to the more expensive animals and refuse the other commonly fed items...Another disadvantage of certain prey is year-round availability...
I would reccomend that you just stick with mice and rats, since they are cheap and easier to come by then say a hamster or a darn anole(unless you live where anoles are abundant)...
I hope that helps