Mice vs rats .. I've heard that rats are more nutritious, and my guy did bulk up faster when he got onto rats .. rats are also cheaper once your snake gets bigger (4 mice @ 80 cents vs 1 rat at $2.50)
As for eating butt first
, as Lisa said, front, back, side ... evidently they figure out the front end mostly by smell (??), so with a frozen mouse I could see them getting confused, I think the little guys just haven't really figured it all out yet, so they get the wrong end sometimes. My guy tried eating a rat sideways once .. he sort of gnawed on a leg for a while, then pulled back and looked at it with a "well THAT didn't work" kind of look.
Live, frozen, prekilled .. there's a 30 year old debate! General concensus is that dead is safer (which IS true .. my guy only wanted live when he was little, but after a mouse bit a hole in him, I went through the agonizing process of converting him to frozen .. well, actually I'm still going through it .. we are in the "I'm not eating unless its live .. you don't eat unless you eat f/t" struggle at the moment. (actually I think he's just fasting .. I wouldn't starve him for the sake of switching food .. the last time I gave in and tried live again he just watched it run around until I took it out ... little jerk !) Frozen and prekilled .. about the only difference is .. how squeemish are you .. prekilled means YOU kill it.