I'll start out by saying I'm a tad biased, as I've been working on a plugin for Openfire for some time now and have had a lot of great interactions with them. That said, I've looked into just about every XMPP server I've seem come around in my day. I've posted a couple of reviews of all of the servers as well. Openfire has always had the best administrative interface IMO, and I've found the code very easy to follow, makes sense, and has great well documented code that's available online. I still think ejabberd beats openfire in sheer speed, but java 6 helped with that a lot. Generally I mostly appreciate the friendly nature of the developers and helpfulness in the forums from them and misc other folk. The plugin architecture is -very- powerful and generally if there's a way for the architecture to be improved, the devs are receptive to improving it.
So far the only other server that I haven't tried is Tigase. Aiming to give that a shot in the near future.
Great work folk!
ejabberd is by far the fastest XMPP server I've ever worked with. It's gloriously powerful and just as they say, fault tolerant. My only qualms with it, and why I didn't give it 5 stars, is that it's configuration is not very friendly to tech heavy admins. In other words, I found that configuring it was similar to configuring many unix daemons and such ... often requires you to know what you are doing. The admin interface doesn't "babysit" the admin much. In fact it typically has you typing in exactly what would be in the config file. The language it's written in I find to be difficult to read and follow, and I take my hat off to Alexey for conquering it! The logs are not very clean to look at either. Hrm. Lots of negative things to say here but let me say that beyond these things it's a glorious implementation and I'm always pleased to see new releases coming out. It's easy to see why this and Openfire are often fighting for that number one XMPP server position. =) The fact that jabber.org chose to go with ejabberd says a lot. Great work you all!