User blog comment:ARZC/Luffy vs Law/@comment-62.72.92.156-20121126143547

This analysis is pre-timeskip, so Haki is left out of the question.

Law's "Room" needs time and concentration to launch, and won't successfully build up if it's disturbed i.e. he's attacked (Vs Pacifista on Sabaody). If Luffy were to recklessly attack with all his speed and strength, Law wouldn't be able to create a Room.

But Law has a blade (Nodachi) which is exactly Luffy's DF's weak spot. But then again Luffy has already fought enemies with blades before, so he can easily avoid Law's.

Conclusion: Luffy wins. Without a scratch.