I only used the word "man" when I'm not happy. "Listen man, I'm not paying for that." "Sorry man, no way"
When I am happy or speaking about something positive, I use "dude." "Dude, that's awesome." "Totally, dude."
I actually don't like people that use "man." It sounds antiquated, like they are trying to hard. On the other hand, I can instantly relate dot anyone who says "dude."