I know you will get a ton of responses here, and I will say I have never shot a buff, so what I have to say is only MY opinion. However I have shot most BHs into north american game and into inatimate objects of many flavors just to see what they will do. I have spoken several guys who have shot buff with the longbow. Last year I gave the ashby modified grizzly a go on 6 deer and 6 hogs and discovered some good and bad stuff. There are several heads that should be strongly considered first teamers to include several new heads like the ashby, the no mercy, abowyer gizz etc. However after much thought on the matter I would prefer the diamond tip Magnus II as it gives the best combination of all things needed. I think a zwicky eskimo or a stos would also be excellent choices with the tip slightly modified. My tests have shown that the tip design on the single bevels bleeds off too much energy, even when sharpened all the way to the tip. On this game you need all you can get.
I spent time at PBS Nashville talking with Monty Browning on this, and he said some pretty insightful things. He is the only guy I know who has put the arrow ALL the way through an adult bull so he is a guy worth listening to. He used the hunter head for a variety of reasons, and for those reasons the Magnus II would be my first choice.