i am looking for a seo plugin. I am using WPMU plug

i am looking for a seo plugin.
I am using WPMU plug in because i have the membership.
WPMU makes a lot of nice staff.
Some time when specialization counts it is maybe better to go with the specialist. or maybe it is only advertisement and nothing more....
But if their is another better one i will like to try it.
In your opinion with is the best ?
SEO Ultimate
SEO by Yoast
wpmu seo?
Thanks a lot for time to answer