What you're looking for has more to do with a given species than whether it's a boa or python. Note that males are usually a fair bit smaller than females, so if size is a concern you should make sure you get a male.
A Ball Python is a commonly kept beginner python, but I would suggest that you do your research well as they are a bit tougher than corn snakes. They can go off feed easily if stressed, so you need to make sure you maintain the right conditions. Also, make sure you get a captive bred one from a reputable breeder.
Personally, if you go with a boa (boa constrictor imperator), I would avoid the more common localities, which can get quite large (10-12 feet). Hogg Island and Sonoran Desert varieties only get to around 6 feet, but are a bit more expensive and difficult to find. Cay Caulker and Cay Crawls are smaller still, but similarly more difficult to find.
1.0 Pastel Ball Python, 1.9 Normal Ball Pythons, 0.1 African House Snake, 1.0 Savannah Monitor, 0.0.1 Argentinian Horned Frog