Which SEO plugin?

Hello,

I have to change my theme because buddypress doesn't support it.

Unfortunately I was using my actual theme (atahualpa) built-in SEO and now I have to think in a new seo plugin.

Which seo plugin do you recommend me to use? I know the very popular All-in-one-seo-pack but as I have to start over I can use any new plugin.

Another related question;
Do you think SEO description updates on my whole site could have a negative impact on my google´s rank?

Thank you for your help,
Luciano