Both are great captives. Both calm down with relative ease - exceptions can always be found. Carpet pythons get their "nippy" reputation mostly because they are pretty quick snakes. Many of the speedier serpents will try to flee when frightened and if that doesn't immediately work they often take a swing or two at the perceived threat. Ball pythons are not fast, they typically do their ball up routine when feeling threatened and only seldom put on the boxing gloves.

Neither are really prone to health issues; when kept right both are darn near bullet proof. Balls will go on feeding strikes, it's just a natural part of the species and something that stresses the keeper more than the snake. Carpet pythons will not live long lives if you overfeed them - that's their achilles heel. If you get a carpet python feed more moderately to maintain good muscle tone and you should be fine.