Seems like you are asking multiple questions so you can gather information by the 'statistics' around RF and then grow a forum, smart. Good luck with your up-coming site, psychology is all about it, read my advertisement tricks thread for more information.
Regardless of that, both systems are decent, IPB is nice actually too but both can be nice. The higher the members are able to give reputation and 'recieve' is a trigger for most people. When they see a big amount of reputation they have, they will visit the site more regularly, so it's the owners job to rep them somewhat high in the start and grow a userbase.
It's much more to it to be honest and not just that. Just a few cents of mine. I haven't posted in a while but you trying to collect answers was something I like of you and decided to reply.
Good luck once again.
]
