I would definately NOT start with a rosy boa. They will be just cruising along and then have a sudden hunger surge and bite you. However this makes them incredibly easy feeders! LOL
Ratsnakes nippy...Sure anything can be, we have Transpecos rats and they are as calm as can be. Very cool as well!
I think corns are pretty cool, we have a few, and are expecting a few this year. Definately a GREAT beginner snake!
What about hognose?? Yes they are rear fanged, however I have never had one even attempt to strike at me, and if they do it's closed mouth from what I have heard.
I realize you said no boas or pythons but have you considered a ball python? We've all heard how they are finicky eaters, however I have found them to be pretty straight forward if they were gotten as hatchlings. However the adult wild caught females we have are near impossible to get to eat!!
I would say a corn is the way to go. ANY snake can bite, you must know this any time you are handling one, and be OK with it. My wife has a Biak Green Tree Python, they are notorius for biting anything that comes close. We have had him for three years now, and he's never attempted to bite.
Good luck in whichever way you choose to go!
Mike
www.snmreptiles.com