Which version of ArcGIS Server?

[BarryGuidry]

We will soon install ArcGIS Server 10, and I am interested in the possibility of customizing web applications with the Viewer for Flex in the future.  Does it matter which version of ArcGIS Server (.NET / Java) to install, to utilize the Viewer for Flex?

Are there pros / cons of either version of Server, regarding the Viewer for Flex?

[LeeAllen]

From what I can tell, there is no difference as far as flex is concerned, since the viewer looks at the Rest endpoints and services created either version.  Considerations include whether you are using Microsoft IIS or another web server app like Apache. I prefer to keep Microsoft products together IIS and Server .NET version.  Others may have more to add.