I really liked my nano puff and I decided to invest in a Nano Air once it started looking haggard.
I have both jackets in size L, but they don't fit that similarly.
The Nano Puff has a 'boxy' fit that I think is pretty comfortable. I like the loose fit because I think the jacket moves better and feels more mobile than it might if it were cut to fit more snuggly.
The Nano Air is cut to fit more snuggly, and while that necessarily a bad thing, it is mostly cut to fit closely through the shoulders and chest. it is kind of shaped like a bell or so.
The Nano Air's face fabric is kind of soft and I think that it is a bit warmer than the Nano puff. That said, they are pretty comparable jackets.
If you are looking into both and hoping to differentiate, I think it is probably worth going for whichever best suits your needs. I've heard that the nano air layers really well under waders for fishing or under a bib while skiing, but I think the Nano puff is better suited to climbing and the alpine.