king snakes are meant to have a bit of a reputation for being nippy, then again all snakes can be nippy, it just depends on the individual snake, always ask to handle the snake before purchasing and you can decide for yourself.
as for ball pythons they have a good reputation as beginner pythons as they are more docile, rarely strike etc but they are also known as problem feeders....
a good tip as everyone knows is not to feed your snake in its tank, preferably remove it to a tub for feeding, this gets the snake into a bit of a routine, and it learns that when you put your hand in the tank its not time to eat and in theory will not strike, but at the end of the day all snakes are wild animals so caution always advised
hope that was of some help, i tend to ramble on