1) Accessibility: WordPress gives me the ability to assist clients who otherwise would not be able to obtain or maintain a website.
2) Plugins: My current favorite is the SEO Plugin developed by Yoast
3) Ease of Use: Just about anybody can learn how to set up and maintain a beautiful blog site.
4) Vibrant developer community: Word Camps, Meet Ups, and lots of online communities.
5) Fun factor: Blogging, expressing yourself, and promoting your business has never been more fun.