Good one. I'm inclined to say Zoro with effort, but it may be too early to judge. We know that Sanji could fight on par with him but seemed a trifle disadvantaged, and we know that Full power Law could dispatch him with relative ease. Zoro should be somewhere in between them as of right now and would thus likely beat Vergo with effort, especially given he has blades and Sanji didn't. I will add though that it's entirely possible that Zoro is slightly stronger than Law. I won't presume that but it's fairly possible given that he is more or less on par with Luffy and Luffy could be stronger than Law. It's all a bit unclear.