for me the demo should only have medium builds, one or two guns, one map, and no online play, only with bots, but not the campaign
Since a big "turn on" about Brink, is merging SP and MP, it would be foolish to only offer SP in the demo. Also, since every map is a map that will be played in the Campaign, regardless how you play (unless they offer a bonus map or special map made for demo) it would have to be a Campaign map.
I say the demo should be 1 map that can be played SP, co-op or MP. Only offer Medium bodytype, but let players know that Light and heavy will be available in the full game. Give access to a handful of guns and a couple abilities, and maybe 2 archetypes to mess with for customization.
I'm debating if the demo should allow players to look at locked weapons, abilities and other items, or to leave them out altogether.