Rowan growls at me and everything else all the time. He's just a grumbly, growly dog. He growls when he needs something (either to be let out, or he knows it's dinner time), he growls if he's bumped in to, he growls when he plays, he just likes to growl.
Riff never growls at me. He growls when he plays, but it's not really directed at me, because he growls when he plays with toys by himself, too. He's not growly in general.