2Do is nice but fairly complex, unintuitive, and doesnt provide the option to present your tasks in iCal. Priorities does it all, and far more intuitively. The high point: the option to see your tasks in iCal. You always get your big picture at a glance, without flipping between apps. Clean, simple, but fully-featured. Priorities really is a gem.
Checkendon about Priorities, v2.3.2