What is the best portable printer for MacBook Air?

Not a lot of information as to what you deem as "best" in your post.

To make sure we can recommend something that fits your needs, could you clarify a few things?

1. What will you primarily be printing? Documents, photos, shipping labels, or a combination?
2. Do you need color printing, or is black and white sufficient?
3. How portable does it need to be? Something small enough to fit in a laptop bag, or is a slightly larger travel printer acceptable?
4. Will you need to print without access to a power outlet? In other words, is battery-powered printing important?
5. What is your approximate budget?

Also, if you know which MacBook Air model you're using, that would help us confirm compatibility. With those details, we can narrow down the options and recommend the best fit.