There's honestly not much of a difference between these two snakes. There is one BIG difference though, that you need to keep into consideration, the size of the snake. As you know, ball pythons, really never get that big, the biggest ball python only very, very rare, will get to be six feet long in a female, but usually stay in the four to five foot range, smaller in males. On the otherhand, you have the carpet, and their average size is pretty big, able to reach up to six and seven feet long, but the biggest one was a 13 foot female. But your average length will be no shorter than six and a half feet in length. So if you want a smaller snake, go with the ball python, if ya like big, then a carpet might be for you.
Both snakes are semi-agressive when they are hatchlings to young adults, with the carpet being just a tad more agressive. If you handle them with respect and not torture, then both will become very highly regarded pets, and you'll have a best friend wrapped around your neck all the time. Of course feeding will be different as well, as the carpet might need rats instead of mice, but ask you local pet store, and they will be able to help you out more, if ya happen to get a carpet...remember, captive bred and greatly taken care of snakes in a nice big cage/tank, will grow till they die, hence a 13 footer in a snake.
Hope this advice helps you, don't fear the animals, just respect them and you will do fine, just one is bigger than the other. Don't get a burmese though unless you want to be the next meal of the snake lol, j/k. Good luck.