Kings are alot like corns...they are generally quite docile, with a few individual exceptions.
Like Katie, I am a HUGE fan of the greyband and mexicana varieties of king as I believe they among the most beautilf AND most docile I have ever handled.
With that said, I also LOVE the Florida king for the size, aggressive feeding responses, and the incredible diversity of color morphs available...almost(but not quite) as many as corns!
As it stands I have 1.2 greyband, and 2.2 Florida kings. The greybands are a typically smaller species, reaching lengths of right around 3 feet, where Florida kings can reach 5-6 feet. Greybands can be a little pickier about eating...make sure you get them WELL established on f/t, or they can be a pain in the hindquarters. Florida kings, on the other hand, will eat just about anything you put in front of them, and they would eat everyday if you let them.
The question of which king is right for you is really going to come down to looks. Which look intrigues you the most? What size do you hope the snake will reach? Do you want a snake that will casually and with time eat the prey you give it, or do you want a snake that might mistake your fingers for food on feeding day, and strike at anything that moves?
With SO many varieties of kingsnake available, the question becomes one of aesthetics, really...which look and size appeals to you most?