Definitely Word press, I did an experiment, recently with two websites, one was wordpress using custom plugins, the other was a PHP script, (blogging) Wordpress won hands down, in alexa it just out performed, anything else in its class, but really a lot depends on what you put into it, I mean if you let it sit there and never do a thing to the site, you really cannot expect much in return. You can get cheap wp hosting, and free themes all over the place, even in my sigs,)
Wordpress is certainly very well optimized for SEO and has a lot of SEO plugins as well. We've always had great results with Wordpress based sites.
You bet? But frankly, I am not sure whether it's the best amongst all CMSes but it is quite very good