Balls and corns have about the same care. Those two are the best starter snakes in my opinion. Kings and milks are a bit more flighty, more likely to bite or musk.
Corns are wiggly noodles, someone who has never handled a snake might be nervous with one, they are active. They are very forgiving in their care, however, and very docile animals. GREAT eaters.
Balls are calm and one of the best first snakes as far as handling. They are frustrating though as if any little thing is off they might go off feed. This can terrify new owners(I myself am guilty of panicking when Maru wouldn't eat for a few weeks)
It's really and truly up to you. As long as you are knowledgeable and willing to match the care they need, you can have just about any of the beginner snakes. Make sure your size enclosure is good, the food size is right, the heat is right, and the humidity is right. Then pick the snake you think is right for you.
Edit: Any of the analogue gauges for humidity or temperature tend to go bad even if they work right at first. It's just how they are made, it isn't accurate enough for care of a snake.