It comes with 8GB, and Leo got that one. There's very little he could do on a computer where he'd see a difference in performance going from 8GB to 16GB. Going from 4GB to 8GB is significant, but the improvements are less noticeable after 8GB.
The one negative that people talk about a lot, is that the display is pushing so many pixels, that there is occasional lag. Particularly when swiping from one desktop to another. It's using the built-in Intel graphics on the base model. They have upgraded the graphics on the newer higher end model, but it's considerably more expensive. Leo hasn't noticed a problem with the base model though, this is just what other people have said. He should really go to an Apple store and try loading full screen apps, and swipe between those to see if that lag bothers him.