Who knows which of these methods of describing lists will win? I’d give a slight edge to OPML, because Winer promotes it a lot. But on technical merit… you tell me. My hunch is XOXO is the crisp, clean and simple solution.

Source: Cloudy Thinking by Ron K. Jeffries » Blog Archive » XOXO & OPML & Simple List Extentions

At the moment, my prediction is that XOXO gets sidelined by OPML, insofar as expressing ideas and data in outline form takes off in general. This will be because all the buzz and work will be driven by enthusiasm and time devoted, rather than technical merit. And, at the moment and the foreseeable future, OPML enthusiasts have the loudest and most active voices.

The only reason I keep bringing up XOXO, though, is that my time is short. To be honest, I've only spent about 8-10 hours in total with all the XOXO experiments I've shared—including my half-baked in-browser editor. Trying to do interesting things with OPML has eaten much more of my time, and with fewer results worth sharing. In my experience, XOXO is so easy as to be almost boring—while OPML has enough sharp edges to seem challenging.

Your mileage may vary, though. My selfish motive in occasionally promoting XOXO is the hope that it'll take off while I'm busy with other things. That way, when I have time to devote to this stuff, there'll already be easy-to-hack XOXO things simmering around the LazyWeb and I won't have to deal with even more OPML in the blogosphere tuple space.

At the moment, though, neither OPML nor XOXO are paying the bills for me. So, if OPML's paying your bills, more power to you!