SEO plug-ins are very useful because they allow you to add custom browser titles (which aren’t the same as your main page heading) and meta descriptions.
I recommend either Yoast’s SEO or All in One SEO Pack.
Exactly what redundancies are you worried about?
I think both of SEO Ultimate and Yoast SEO are pretty good. And lots of their features are more or less alike except few differences, such as Yoast has XML sitemap generator and some other pluses. I found this article on the comparison.
I think you definitely need SEO plugin to succeed in search visibility. Its best to study SEO beyond plugins though, I would recommend this book: SEO – An hour a day. This will give you a basic knowledge of what SEO is and how to position it strategically on your website.
