A high quality chalkboard with good chalk is the best. writes like butter, not much dust. much easier to shade or draw dotted lines. If you get way to intense you just snap a 5 cent piece of chalk instead of ruining a $1 marker. Plus your work just pops out of board as if its the only thing there, easy on the eyes, no reflections etc.
For a lecture hall, hands down chalk is the best. If you have a small room then I see the case for the whiteboard.
sparknotes: Chalkboard FTW!