Apple's 13-inch MacBook Pro vs. the MacBook Air: Which one should you buy?

Apple quietly launched a new version of its 13-inch MacBook Pro on Monday, quashing rumors (for now) that it's working on a 14-inch Pro. 

The new MacBook Pro starts at $1,299 and has an upgraded keyboard and more storage. For big processor and memory upgrades, however, you'll have spend $1,799.

This makes it an interesting...