Every Sunday and Wednesday my church streams the church live over the internet in a WMV format. But this requires everyone watching or wanting to watch to have Windows Media Player. So would it be better to offer streaming in in every format, (Quicktime, RealPlayer, Windows)...or what do you think about streaming in flash?
Streaming in (format X) will require that any viewers also have a player for (format X). Flash requires a Flash plug-in, WMV requires Media Player, RealVideo requires RealPlayer, Silverlight requires (whatever the Silverlight plug-in is called), etc.
What it really comes down to is:
1) Which format is supported by your server?
2) Which format can you produce?
3) Which format has the smallest bandwidth requirement?
4) Which format is used/will be used by the majority of your viewers?
Maybe you could add a quick survey to the site, or just ask them, to get an idea of what formats they want to see.