Mac Air is for those who want swift performance and long battery life in a lightweight machine for a reasonable price. Power users and photo and video editors should step up to the 13- or 15-inch MacBook Pro, which offer very sharp Retina displays along with beefier processors in heftier designs. While more expensive, the 15-inch Pro is really the only choice for those looking for workstation-class performance.
The 12-inch MacBook is a niche system. It's the most portable choice in Apple's lineup, but it also costs just as much as the 13-inch Pro (which offers more speed and a bigger display) and it's $300 more than the 13-inch Air (which has more battery life and ports). So get the MacBook only if you want to travel really, really light. For the vast majority of shoppers, the 13-inch Air continues to be the best choice, but the 13-inch Pro is a close second because of its better screen.