I am now employed by a Moodle Partner, so perhaps my list is a little biased. But bias or no, Moodle is a better project, platform, LMS, and community than Sakai.

• Better community. The Moodle community is just
• Better resources. One central Moodle resource, Moodle.org. Sakai's resources are spread all over God's Green Internet, and it is nearly impossible to find anything.
• Better design for Teachers. Moodle has an easier to use, better pedagogical design than Sakai. (need refs)
• Written in PHP. Okay, so, maybe the J2EE platform (used by Sakai) lends itself to better performing, production code, but PHP makes Moodle easier to dive into (well, not always a good thing), easier to customize, easier to install, easier to configure, etc.
• Better support. Moodle's Partners offer more complete, less expensive, and more innovative support and hosting than what is available for Sakai.
• A single strong, charismatic, energetic, driven, and innovative leader. Sakai needs a Martin Dougiamas. Any really successful Open Source project does, (or at least needs a *small* oligarchy of leaders). Linux, FireFox, Apache, etc. I don't think Sakai has that. Sakai has a foundation. Sakai has founding partners. But Sakai is missing the key principal with veto powers.

Okay, I need references to back me up. I need to expand on these items. I need maybe some more bullets. But this is a good start.