How to select a dissertation committee member wisely? I'm currently developing my dissertation proposal, and am in the process of choosing my committee members.  I have heard that one should carefully choose their committee members, since they ultimately judge if and when your PhD work is done.  As far as I can tell, a committee member should at least have some expertise in my research topic.  I'm sure there's more to it than that, but I want to know what other qualities should I look out for?  What qualities in a committee member should I avoid?  I imagine these other qualities are subtle and difficult to judge at first.  Nonetheless, how do I know if they are a good fit for the success of my PhD?
First, ask your adviser.  He/she likely knows more about most of your department faculty than you do.  You don't have to do exactly as you're told.  But if you don't, this should be an intentional choice on your part, and you should have a good reason for that choice.  Beyond that, I see at least 3 broad areas to consider.  You want committee members who will


strengthen your professional network: introduce you to potential collaborators, and possibly help with your search for a postdoc or tenure track position; and/or write a letter of recommendation for you
give valuable feedback on your work: you think they'll actually read your thesis (you might be surprised how uncommon this is), and might have something constructive to say 
be easy to work with in the defense process: likely to be flexible on the date of your defense, and likely to sign off on your dissertation without demanding lots of changes (fitting into 4 schedules besides your own can be a nightmare; it's nice to have a few committee members who are easy to work with on this)


Which of these contributions you value most will depend on what you're hoping to do after your PhD.  If you're looking to move into industry, many of your professors' contacts may be less valuable to you than if you hope to stay in academia.  Do you plan to stay research active? In the field of your dissertation?  Practically, you may have limited options.  At the very least, you should weigh 1, 2, and 3, and estimate how you think each candidate will contribute in each area.