Talker is more extensible, we're focusing on API and plugins http://talker.tenderapp.com/faqs/api, has inline feed notification for eg.: github commits, twitter search results, tickets updates in the chat room. And a lot more to come.

Talker also has a free version (4 concurrent users) https://talkerapp.com/signup/free

Is campfire really in development any more? Seemed a bit of a dead project last time I looked.