Garters can be a bit musky and/or bitey. If you go that route, definitely research the differences and choose a species that best fits your expectations as a keeper. Bulls can be intimidating if you're not used to big and loud threat displays - most chill out naturally as they get more accustomed to their keepers or, if you work with them a bit, they typically calm down real quick. Ball pythons require more specific care guidelines and their fasts can be worrisome for new owners. Out of the 3 you listed, bull snakes will probably handle keeper errors and stress the best so they get my recommendation.