He has proven he can defeat each one easily individually but all three. He would have to use his force powers and with that I say dooku wins. I love dooku but I think with the combined efforts his lightsaber won't by itself do the trick so he would need his force powers. He may loose one considering facts dirge can regenerate.
If you take out bill and if he can dispatch ventress quickly then grevious than surge is in deep trouble so I give bonus round two to dooku.