Well in the end it always should come down to what appeals to you personally so no one can really advise you on what's the better first snake.
Corns are gorgeous snakes and do come in a ton of lovely colors. They are a pretty easy snake to care for but are faster and smaller and tend to be escape artists. Balls are great also but do have more specific needs as far as temps and humidity to do well. They tend to be a bit more shy but with careful handling they don't really deserve their reputation as "sitting there in a tight ball and do nothing" snakes. They ball up as a defensive mechanism so if they are treated right and slowly get used to being held, they don't really do that all that much.
Of our 5 female balls, we have a range from some that are busy busy snakes and explore constantly when out, to others that like to hang out with the warm humans to one that is not tolerable of any handling. Only one of these snakes however was raised by us from a young age so I'd advise you to get a young snake from a reputable source that has been well started and is healthy and eating well if you go with a ball (that really applies though to any snake purchase).
Good luck on your decision. Take your time now and do the research and ask questions and then you can make the right choice for you and the snake.
~~Jo~~