Definitely should do a Master Chief-Batman showdown. Fist fight only, two supposedly humans at their physical peak and only their base equipment (so no satellites Batman).
This is exactly what I was thinking about. Both are supreme tacticians and strategists. Batman has the advantage in resources, but Chief has the advantage in strength and reflexes. We've seen how incredibly adaptive and resourceful the Chief is, but we also know that Batman is incredible at finding out his opponents' weaknesses and setting up a trap designed to take advantage of it.