Milks, kings, corns...they're all pretty much hyper and/or super-paranoid as babies. There are exceptions, I'm sure, but the general rule is that they are quite flighty, hissy and nippy. You might try keeping an eye out for a mature specimen of any one of these. Then you'll have a preview of its adult temperment and a much better chance of getting a snake that is a good fit for your family.
As for the RTB...I guess it depends on what you're looking for. The most common is the Columbian BCI. They're pretty forgiving of husbandry mistakes...eat like crazy...and are generally quite well behaved once they're past that frightened baby stage. (From all I've read...I've never owned one myself.)