Just spoke to a guy at Camcoat (think he was the same guy I dealt with for my Buell headers - very nice chap)
He says both should be fine. When I suggested someone on the site had had issues with flaking he said that it's more likely a one-off problem, probably something to do with bad keying. Anyhoo, it's not really for me to comment on and without specific details not much he can comment on either - at the end of they day, coating exhausts is what they do day-in, day-out, so I'm inclined to think they probably know what they're doing.
He did say, however that the black ones provide more heat insulation that the Kermachrome, but that either should be fine.
Black, chrome, black, chrome, black, chrome... black...?