If you exclude the core plugins, All in One SEO Pack is the most popular WordPress plugin of all time, having been downloaded over 14 million times.
All in One SEO is so popular because it appeals to both beginners and experts.
For beginners, All in One SEO works out of the box with very little configuration needed. Also, as the name implies, it eliminates the need for multiple plugins because it contains many key features such as handling metadata and installing Google Analytics.
For experts, it offers a lot of flexibility for setting up your metadata and integrates smoothly with a wide range of other extensions.
We covered All in One SEO back in 2011. Here are 2 new videos tutorials to get started with All in One:
All in One SEO video #1
All in One SEO video #2