Personally, I like boas better than balls. They are much more active, and are more fun to handle. Boas are also better eaters and will take frozen / thawed rodents, while many ball pythons are picky eaters and will only eat live rodents. If you are worried about size, male boas stay much smaller than females. There are also dwarf locality boas out there that stay fairly small. Some grow no longer than five feet.
Hope this helps.