I think for me, IRL, M is definitely more of a Dom, simply because he loves to dominate, and it's ingrained in his personality in ALL things, so it's something he really can't avoid.

I don't ever refer to him as Master, and I think for us it's the power balance.....we work together, and he fully EXPECTS me to have opinions, input, and even stand up to him when I think he is wrong (I'm speaking mostly in business scenarios here, but even in our sexual/personal relationship, he would not respect me if I didn't voice my opinions, no matter what they might be). He doesn't want to master me....he likes dominating me, which implies that he has to work for it a little more. lol. That's likely just us though.