I might be missing something fairly obvious or being someone that believes in the eye test way more. But McCann is hitting .286, Avila is hitting .182. McCann has one of the best CS% in baseball. When McCann is at the plate, he LOOKS like he knows what he's doing. Avila is so far from contact it's beyond scary. Avila's a career 242 hitter, skewed massively by one very good year in 2011. The guy is a walking ambulance, he cannot stay healthy for an entire season.
McCann probably won't be a perennial all star, but he gives you a much better chance to win than Alex Avila.