Kuiu 15 bag, or Marmot Helium.

[Bushcraft]

Kifaru's Climashield APEX is pretty amazing. I've been rocking one of their Parkas since they first came out.  It was a gift from Patrick. They have since upgraded the insulation (and a few design tweaks) with the release of the newer version.  Company bias aside, it is one of my all time favorite pieces of kit.  It's literally like throwing a sleeping bag on in terms of added warmth and comfort.  In fact, I use it and a Doobie on trips where I know the temps will not get much below 40 degrees and sleep well.

this seems rediculous, your doobie is as heavy as 2 20* quilts.

Oh, I'm not suggesting it's the optimum gram-weenie solution by any means.  There are definitely lighter weight sleeping alternatives on the market. It's simply what I had on hand and preferred the leg room over the 5-6 other sleeping bags I own.

That said, if/when the proverbial poo hits the fan, I'll take the weight penalty of that synthetic Doobie over pretty much anything made of down.

[Stein]

For me, it depends on the temps.  If it is consistently below freezing, I go down - always.  I have been in them sine the 90s and they keep me warm and I don't really baby them or loose sleep.  I also haven't had any problems with condensation or moisture at all.

I have had tons of problems with synthetic loosing loft - all the time.  Leave it compressed, leave it in a hot car, run it a few years, it all degrades them pretty quickly for what I paid.

I have a giant Marmot bag from about 97ish with a gore tex shell that hasn't lost much, if any loft.  In a bivy sack, it is good to -20 in the Bridgers and I use it all the way up to +20 although I do want a second bag for lighter weight and packability.

With the quality of bags, down, backpacks and tents, stuff just doesn't get all that wet.  When I was camping in a surplus Korean war tent with no floor in Boy Scouts, it was a different story.