This link show features of XMPP are implemented on agsXMPP http://www.ag-software.net/index.php?page=agsxmpp-sdk
But it seems not latest information. You can compare these features with XEPs are implemented on trial-servers.
XMPP is a standardized protocol withing the IETF. agsXMPP works with every XMPP compliant server. There are no known problems with any of the available servers.
So the question is not "which is the most compatible server", it more which XMPP server fits bets for you and which features do you want to use. There are over 200 XMPP extensions now. Some of them are client only, and some of them need special code in the server. So you should find the correct server based on your requirements which can be:
Thanks your reply. I want IM (client, server) which can be file transfer, conference and voice chat. I don't know how to begin. Can you give me more detailed advise?
download a existing XMPP client [1], register an XMPP account (or 2) on a public server and play with several functions. I suggest clients which have a debug console, so you can also look the XML which passes the socket and learn the protocol.
Now its time to get started with development. Download and install a XMPP server [2] on your local developer machine and configure it. Ejabberd, Openfire or Tigase are easy to get started with on Windows.
After you have installed teh server try to create some accounts and login with an existing client.
If everything work fine on your server open the MiniClient example from the agsXMPP SDK and connect with the example to your local server.
study the MiniClient code and start your own development. You can extend the MiniClient code or start a new client from scratch.