I'm not saying one is better than the other. I'm just trying to figure out a pet store employee thinking a snake is depressed. Surely this guy is smarter than that!! The only thing I can come up with is that he is trying to make a fast buck! The live "pet mice or rats" tend to cost a bit more than f/t. At least in the pet stores in my area.
You get your snake eating on either one that you can and you and your snake will be happy. No need to call Dr. Phil over this one!