Best growler..

Without a doubt, Mikael from Opeth. Aside from have a style totally appropriate to the music, he can do that and play some great guitar at the same time. Being a guitarist, I know it's a bitch to coordinate that and I have to give him extra credit for that, aside from the fact that he growls great.
 
Personally I like the older growlers like Jeff Walker/Bill Steer, Kam Lee, Ross Dolan, Glen Benton, David Vincent, Chuck Billy and Donald Tardy. Chris Barnes when he was with Cannibal.