Most systems are now of the outboard bearing design and the rest (ISIS, ocatalins and square taper) are dying off quickly. It's not wise to invest in a crank that requires a BB that is nearly impossible to find.

A lot of the outboard designs had problems in the early years, but most brands have finally got the bugs worked out. There are some outboards cranks to avoid, due to known problems, like FSA models of just a few years ago.