Handleability
Ball Pythons are fantastic to handle. They do not tend to move around very quickly when relaxed, and have shown to be very tame pets. If they become quite accustomed to you, there is a high possibility that they would quite happily sit around your neck while you watch TV or get on with day to day things. They do have fangs, however they are not venomous, and if they were to bite at you, so long as it was not in a sensitive area, it is highly unlikely to cause great harm.
Size/Colour
Ball Pythons at their absolute maximum can grow up to 6 feet, though this is uncommon. Most only grow to 5 foot, so are quite a manageable species. Where colour is concerned, there is a huge market for the variations in colour and patterns that a Ball Python can be. Normally in the wild you would see the usual brown/tan/yellow/black hues, but as they have been bred in captivity, they have been bred to bring out certain markings so there is a huge variety available.
Diet
Ball Pythons and most snakes in general are easier and more difficult to feed at the same time than other reptiles. On the easy side, you only feed them between 1 and 2 weeks, though they can go longer. On the difficult side, they eat either live or frozen thawed prey, consisting of mice, from babies to adults. Bigger snakes will also eat rats, rabbits, or larger, though very uncommon. Live prey is not recommended as a live animal can damage the snake while they are trying to eat, sometimes quite severely. Killed, frozen and thawed prey is always recommended, however if you have a snake which has been accustomed to eating live, it can be difficult transitioning to frozen thawed meals.
Habitat
Ball Pythons are semi-arboreal, which means if there is a branch to make use of, they will, however they are just as happy curled up in a sheltered enclosed spot. There are two main ways to house a ball python. Some like to keep them in a vivarium of no less than 2ft, with plenty of hiding spots so they feel secure. On the other hand, if you collect a large number of snakes, some people make use of snake racks, with heated plastic 10 litre tubs. Personally that is not something I would do, however it is a very common practice, and so long as the snake feels safe, that is the most important thing. Ball Pythons need to be kept at around 30*c/80*F, and humidity at least 60%. They also need a rough object like a rock to rub their scales on, as this is crucial to help them shed well.
Lifespan
These snakes can live upwards of 40 years with proper care, so if you are going to get one, make sure that you are committed to do so and will be able to look after it well into your own old age.
Experience Level
Ball Pythons again are a great beginner pet, and a great foray into the world of snakes. Some help may be required for those who have never fed live/frozen thawed prey as it can be a little daunting at first. Only experienced keepers should look at rescues as these rescued pets can have health issues which can be difficult both time wise and financially.