Personally, I began using PPRune when I was working in New Zealand and brought it home with me - so I was using this site long before I even knew forums like AvCanada existed.
I've never been a big AvCanada fan and left when I realised it was really just a bunch of 'chip on their shoulder' kind of posters who were more interested in making stupid comments and stirring gossip, rather than providing information.
I guess the big catch for me here on PPRune is what Rhys Perraton was getting at:
PPRUNE has some great stuff such as Aviation History and so on and many people seem to be on it because they have a real interest in, and enjoy, aviation.
You actually get an answer that is professional, rather than sorting through 10 posts of "how the hell do you have a license?" type responses before finding one, tiny shred of information.