Ball python because they don't eat bugs or need a complicated set up like a beardy does. Not heat lamps of UVB lights needed. No speacial vitamine supplements to buy etc.
Mind you if I was going to pick a snake over a beardy there are about 6 other snakes I would chose before I would chose a ball. I've got about 10 balls right now and if I wasn't trying to produce an albino I wouldn't have any, maybe two but that's it.
Other great pythons to consider instead of a ball would be a childrens or spotted python. Jungle Carpets don't get much longer then a ball and are a much better python IMO. There are also lots of great small boas to consider too. Rosy Boas, Sand Boas, Rubber Boas, Hog Island Boas etc.