I have read that it is technically more efficient to have the most teeth contacting the chain. This was specifically in relation to SS gearing, where it was determined that more teeth = more efficient, despite the slightly increased weight. Personally, I didn't understand the physics when I read it, and would think more contact area would mean more friction, but apparently that is not what was determined. On a geared bike, however, I would agree that whichever combo gives the best chainlinewould be best.