Is Dead Pool a good guy?

He's not considered one of the X-Men nor part of the Brotherhood. Meaning: he's neutral.

Basically he is a mercenary, which means that he will do whatever the person paying him tells him to. He does however have a consience and so is often seen working with the "good guys."

Technically, Deadpool is a mercenary, thus at the end of the day, it's all about who is signing the checks. He has been shown as being a member of the latest X-Force, though.