Hi Marcus.

I agree with the previous answers. Just stick to one plugin. Besides, WP plugins use up server resources so try to keep only the really necessary. Personally I use Yoast's and works well. Make sure you have the latest version (0.4.2) since the previous one gave TONS of errors when trying (failing) to generate the sitemap xml.

Yoast's plugin is particularly good since everything is integrated, so the sitemap is coherent with the canonicals and the noindex etc etc. Otherwise, you'll have one plugin dictating, say, one canonical for a page and the other plugin a different thing (hypothetically, at least) which is obviously not good.

Good luck