I always find MTB bars to be less comfortable than either Northroads or drop bars. Reason is that the position of the grips forces the arm and wrist to twist somewhat. Over long rides this can be painful. However, bar ends do help this quite a bit.

Actually, if you are having wrist or arm problems, the Northroads bar might be the most favorable. The position of the grips is more natural... less twisting.. and you can take advantage of the bar bends if you need to stretch out.