only ever used wordpress... great script, great community and loads of mods available... the akismet spam filter is also great!
I use Wordpress, but I have used blogger and livejournal and found them both very restrictive. LiveJournal I hated - whats more ugly than ads which you don't even earn any income from!
Before I set up my blog, I did a lot of research on blog scripts. I chose WordPress because of its ease of use, readily-available themes, great plugins and other feature enhancements, and tons of community support. All over the web, people consistently chose WP over other blog scripts. So far it's all I'd hoped it would be and more.