Member of the year could be a good one. How would you rank that? Just on their overall quality of posting, attitude, helpfulness etc.?
Maybe you could do member of the year for all three of them.
Example:
Member of the year 2008: Quality of Posting; Member with best quality of posting, Staff member with best quality of posting
Member of the year 2008: Attitude; Member with best attitude, Staff member with best attitude
Member of the year 2008: Helpfulness; Most helpful member, Most helpful staff member
etc.