So... not completely going to discount the other posts but more some apples to apples perspectives and numbers for you. I am a big fan of this jacket and finally got a nano-air this year as well (waited for the 50% off sale).

This is a synthetic piece... so all the basic down vs synthetic logic or arguments apply.
Specifically, this is intended as active insulation (IE you may sweat) as opposed to camp insulation.
If you want a "Stop piece" for camp... pulling out a down puffy when your activity is done and you want a one and done piece then down is better in terms of warmth to weight ratios.

More specifically the apples to apples then is not down, but Fleece. it still works when wet, isn't affected much by body oils, and will hold its basic loft when layering (things down will not do).
So if you compare it to a similar weight fleece like a 200 weight R2- http://www.patagonia.com/product/men...fleece#start=1
You'll see a more accurate weight comparison 14.3 oz versus a 11.9 oz nanopuff jacket.
You could also look to the newer pullover version too to save a bit more weight- 10.1 oz- http://www.patagonia.com/product/men...&start=1&sz=24

Compared to a fleece product- the bulk of a PLG synthetic is much closer to down.

By the numbers:
60g of PLG= 1.84 CLO (About 48.75* rating)
A 50* EE prodigy in 2.1 Apex is 1.64 CLO and rated at 50* as a sleeping quilt.
Now to be fair; the brick quilting on the Nanopuff is extensive so puts those closer in rating the unquilted Apex (if not worse) so it's reasonable to call that (with a light baselayer) a 55* jacket on it's own.

Now a similar down jacket would be extensively sewn through quilted as well so a micro puffy (UL) down is a bad comparison... those are closer to a 100wt fleece. You really have to look at one up to compare-
Keeping the company the same- it falls between a down sweater at 13.1 oz (closer to 300 wt fleece in warmth) and a UL down jacket at 9.5 oz.
http://www.patagonia.com/product/men...ests-insulated
http://www.patagonia.com/product/men...ket/84757.html

So...
Do you want something you could safely wear on trail or with the risk of getting wet?
Or do you want a stop piece that you will baby a bit and keep dry?

I prefer to layer my windshell over the nano-puff personally- though I wear it most often as a standalone daily jacket for most of the year. I may wear several layers under it but expect it to give me a 15-20* bump in warmth over what I am wearing. The reason I prefer it; I can beat the crap out of it. If I catch a spark by the fire I won't have a geese fart of feathers. If I snag a branch gathering wood- I stitch up the shell when I feel like it. But this shell is pretty tough stuff. I did slice the shoulder on mine carrying metal studs and just left it to see. A year or more later and it hasn't run or unraveled much beyond the initial snag. It has dirt and grease on it. I don't over compress it so it has held up decently over about three years. It is 92% warm when wet and dries under body heat.

All that said... if I just wanted a warm jacket to put on to sit in the shelter and wait for my freezer bag meal to heat while I read the journal:
A down jacket will be warmer, pack better, and be lighter.

But if I want a piece of gear I can use and abuse- I choose the nano-puff.
The nano-air seems a bit warmer and has better stretch... but I'm not sure about the durability of the shell or the reduced quilting as that is unproven. That jacket is designed for alpine climbers though who will wear it with a WPB shell-so it's shell is made to slide easily into another jacket. The nano-puff is a much better outer layer for camping/backpacking.

As to other options...
I'm a big fan of the Cap 4 (now thermalweight) as an insulation layer for most backpacking trips at 6.2 oz and layered under a windshell.
http://www.patagonia.com/product/men...weight#start=1

unless I know I will be camping more and/or it is actually winter or late/early shoulder seasons... I don't bring a puffy jacket of any type. My 45* synthetic quilt serves that purpose for camp wear.
But on a more casual trip or winter backpacking trip a nano-puff is what I choose, especially when it's handy for the first hour or at breaks when moving. And at home -this (or the nano-puff now) is what I reach for to walk out the door all winter.

I don't like much more than a vest in down. I think that does more for you than a jacket and you aren't likely to get that tangled in the brush or fire.