Donna and Rose. Always Donna and Rose. Martha is wonderful, but she isn't the "save-the-Doctor's-ass-because-he-can-never-save-himself" type. And Amy is wonderfully headstrong, but there haven't been many opportunities for her to save Eleven.
The Doctor and Donna Noble. I completely just fangirled over this, because they are beautiful and wonderful and amazing and I miss them both so much. (Though I don't nearly love them as much as Ten and Rose!