1.) So what’s the best SEO WordPress plugin?
All In One SEO is definitely one of the best known which is why so many people recommend it and I’ve used it without problems on a variety of sites and hosts so I wouldn’t be too concerned about resource usage as mentioned in a previous answer. Ultimately if it doesn’t work for you you can uninstall it and try something else 🙂 It is a pretty good plugin IMO.
The most comprehensive SEO plugin is probably WordPress SEO by Yoast (link below) which has a multitude of options and settings to play with so it’s also one of the most complicated. Is it the best? Not necessarily but it is laden with features.
There is no simple answer to “the best” really, it comes down to experimentation and finding the plugin or combination of plugins that work best for you and your sites and that you find the most pleasant to work with. There are so many to choose from and none of them take care of every single optimization strategy so often a combination of several plugins ends up being commonplace.
I’ve listed a link to the plugin repository below based on a search for “traffic + SEO”. This only provides the free plugins of course and their are countless paid solutions too that vary in quality and effectiveness but there are certainly some very cool ones that do things none of the free plugins can.
As a point of interest, it is often better to have a properly optimized theme which will do away with the need for many of the SEO plugins and help a site’s load time etc. I stopped using All In One SEO for example when I started using an optimized framework but I still use a couple of additional plugins to help with very specific SEO settings and tasks. I particularly like WP Traffic Force (no longer currently available unfortunately) and SEOPressor was very good too. Other plugins are very task specific, building backlinks, optimizing and structuring keywords and internal linking, increasing visitor interraction or social media integration etc. they all may have a role to play on your own sites or they may not. The beauty of plugins is that they can be added and removed with a few clicks and with the free ones at least, you can’t really lose.