I previously worked in a large, not-for-profit organization that used Diligent. The system worked well and the 24-hour call line was very useful as we first transitioned to the system. However, the cost per user is very expensive, given that very little support is required of Diligent once a user becomes accustomed to the system.
I recently joined a small, not-for-profit regulatory organization that uses BoardVantage. So far, I like it and find it easy to use. Our Board is also small, only 9 members, and I provide sole support.
Hope this helps,
Mae-Yu