I've used both extensively, and my favorite is Yoast's SEO for WP. It has some nice features like setting up your site with Alexa, Google Webmasters and Bing webmaster tools easily and also a Twitter card. It gives you visual feedback on how SEO-friendly your post/page is, and over time I've found I have learned to write better posts SEO-wise more quickly because of it. He updates it a lot, and adds nice features that users ask for, and it plays nice with other plugins(no conflicts). It's one of my favorite plugins, actually.