My friend ask me this...IMHO, I think Luffy's haki is stronger. Because I told him that Luffy has Haoshoku Haki (Conqueror's Haki). Maybe DoFlamingo also have this because according to Chinjao, a lot of pirate have that in GrandLine. But then again, DoFlamingo hasn't show it (or did I miss it?)... Anyway, I hate DoFlamingo big time. Same level as Marshal D. Teach.