I think Matt Smith works best with kids. His scenes with young Kazran in "A Christmas Carol" were his best work. Young Kazran should have been his companion. Smith is very much like Troughton. Troughton was at his best with Jamie McCrimmon. Frazier played that role as if he was just a kid. Zoe was basically just a kid too.
Eleven needs his version of McCrimmon, imo.