What combination of power pieces would you trade for a queen?

If it gives me a better position, I would give up two rooks and a knight.

If position is not in my favor, I would give up two bishops and a knight

If it gives me a better position, I would trade all my material away.

An IM friend once dropped his queen for 2 bishops and a pawn (back when he was maybe class A)...and though he had not even seen he would lose his queen, it was a winning sacrifice on purely positional grounds, since all of his pieces became activated in beautiful harmony.  Er well, I guess you cant call it a sacrifice if he didnt see it, but you get the point.