Im building a video/pic site and wanted to also build a community around this.

What do you think is better to use a forum or groups - which is a better format to support user interaction.

Im thinking to start with a forum is better to get the discussion happening but once people start using to more transitioning to group would be better. Forum is a silo on it own contains all discussions whereas groups as each individual silos.

I like the idea of breaking things up into groups which people can join if they are interested. But again if there is not much discussion going on groups might be pointless. The other thing I could do is make 5 main groups to start the site and then let users add more. So everyone that joins is a member of those 5 automatically.

The site is about health and fitness.

thanks