in my opinion WebORB is better, but you should attentively read the licence for it. If it's ok for you, choose it, otherwise Fluorine is what you need.
If i Use WebORB then which version should I use?
Community or EnterPrize?
I just want to pass remote objects from client to server?
If you just start, download latest version (3.6).
Community version is free (read licence to understand limitations: 5 connections is allowed without registration for developers, for more you should register your copy, now it's free), Enterprice is not free - so it should be your decision.
FluorineFX and weborb are faster as they are remoting. Web service will be slower.
Fluorinfx is free and opensource. Web orb is not free for redistribution.
You can refer to the document at http://blog.ancheril.net/2009/09/flash-net-remoting-using-fluorinefx/