I agree that Doflamingo wins this one, but I can't agree that he wins this with eaze and by a big margin.
Even before timeskip Sentoumaru seemd quite a high level fighter in World Government structure, but now he seems obviously stronger fighter and we have yet to know his rank among Marines. Of course he should be weaker than Doflamingo, but I obviously can't agree that he will defeat Sentoumaru easily, especially since Sentoumaru has a great Haki abilities.