I prefer Quicktime since it's free and works great. It's also easy to prevent hot linking unlike other formats.
I think you are talking about broadcasting movies, but on the subject of live steaming I just set up live streaming for Luna on her paysite using this software,
http://www.nuspectra.com/products/sitecam/index.htm
Seems to work real well and if her memberships grows beyond what her ADSL will handle they have a server that rebroadcasts her feed for a $1000. that should handle just about anything.