User blog comment:Sosuke Aizen008/Who is the most powerful in stern ritters?/@comment-11051098-20130921201638

As far as we know, the letters signify a special skill each Stern Ritter has. So I don't think they are ranked in the order of strongest to weakest from A to Z.

I don't think we can determine who is the strongest yet. There's still 4 Stern Ritters who have not been revealed, and 3 more who's letter we still don't know. It's too early yet.