Middle Tier for a Flash/Flex app

Hi folks,

I had posted over in the ServerSide forum and just wanted to get a consensus from you flash/flex folks too. Just needing some general input (pros/cons) about hooking up a flex application to a service layer. Here is the original post (http://www.kirupa.com/forum/showthread.php?p=2230914#post2230914)

Here is the list I have been investingating:
[LIST]
[]RubyAMF
[
]Liverail
[]Red5
[
]Fluorine[/LIST]
Thanks,
Justin