I use Platinum SEO, but only because of recommendations I got. Can't really compare with others to be able to give you comment based on my experience.
All in one seo plugin Joost de valk or the new plugin that has all the features of all in one seo plus robot index, no index etc.. ! Google it. Another option start using thesis theme, it don't requires any seo plugin. I'm using it on many of my blogs and i'm really happy with the results.
There's a free seopressor clone available at bloggerhigh.com. They also provide a free autocommenting plugin.