If I'm not planning on doing much typing, the iPad Air is preferable for most situations. However, if I am going to be typing more than a little bit, I prefer my MBA. The only other time that I'll generally opt for my MBA over the iPad is if I'm multitasking (e.g. watching Netflix and catching up with the news, etc.) or when I am doing chores around the house or something and want to put my MBA on the counter and watch media or something. The MBA has pretty good speakers so I like it for those scenarios.
For casual social networking, though, the iPad Air is a fine choice.