Top channel criteria should be based on activity yet memes channel with 4 members and 55 posts isn't in the top category while channels with 50 members and almost no posts are listed. It should be based on activity.
it's a bit tricky because it could be that one person is posting 1000 posts in a channel. This is not really desired because the person is using the channel like a blog, not a discussion board.
On a more fundamental level, this is a problem of discoverability, and this doesn't have to be based on rankings. Will try to think about this more.