CEOs, Founders and Leaders, who would you hire?

Would you prefer a coworker that is an observer or one that is a doer. Some people are keen on observing what's going on and absorbing all the information. Maybe they're less enthusiastic to proactively do things. Being completely prepared is more important than to do a mediocre job. People who are more enthusiastic about doing, and creating may focus more on the action than the learning process. They'll make mistakes but they'll learn from them. Ideally there should exist a balance between the two, keep learning and observing and proactively do things, sometimes even if you've never done it before, try. But if you had to choose, who would you rather work with?