I'd like to nominate Tom Au.
Tom has lots of experience on a wide range of SE sites; he's a real veteran. Even a quick glance at his network profile will give you an idea of what he's like.
Tom also has one important quality: He's been active on Engineering throughout the private beta, and his questions and answers have covered a whole bunch of topics. He may not be proficient in all of them, but he has a very good overall knowledge of engineering - despite not necessarily being an engineer! (?)