I guess, here we go, to be a little more clear
Ill clarify for the op, I don't have nearly the experience some of these guys do. Some of these guys have probably spent more time backpacking than time that I have been alive. That's not to say my experience with my bags is not valid, nor does it mean that I am stupid to use synthetic (though there are a few people would vouch on the stupid part!) It is simply my preference.
I will say this, down is not a bad choice imo for a sleeping bag, that's going to be used only for sleeping in. Obviously down is the majority. While I don't have the nights in field that some of these guys do, I have spent a good handful of nights living off my back, and I think iv spent enough to figure out what I prefer.
I guess ill outline a few reasons why I like synthetic over down.
-No worry about leakage, snagging fabric, or poking holes. Iv put small rips in a down bag, along with gotten small holes, from sharp grass, causing leakage. Holes in down need to be patched fast, where as synthetic a small snag is no big deal, nor is a burn hole. Im speaking now of marmot bags that I have used in saying the outer fabric just is not as tough as what I use in my kifaru synthetics. My marmot down bags were just not as tough as my kifaru synthetic, period.
-Loft does not degrade as it gets wet in synthetic. Wether it gets wet cause I was stupid, or from extended nights of getting in it damp. Once I got my down a little damp, I didn't care for the feeling of sleeping in it. Loft degraded, and I was now spending time trying to dry some of the more wet parts of my bag. This is not coming from a backyard test, but week long trips living off my back in various areas in the lower 48. Condensation would accumulate and the down would get damp. Down holds moisture, fact. Is it a problem most of the time? Probably not. Maybe more of a nuisance than anything. But packing up my damp bag, only to be pulling it out, damp, day after day was not my favorite. Did it still work? yes.
-Down did not seem to dry me like synthetic does while im in it. Synthetic has always left me with a dry feeling, wether I got in it wet, or dry. In my synthetic stuff id purposely go to bed in my wet pants, knowing ill wake up dry.
-Down straight up stinks after a few weeks of sweating in it. And IMO its a pain to wash, not only that but putting my 400$ bag in the dryer is pretty nerve wracking as well. With synthetic I just wash, and let air dry. Easy. Not only that but synthetic didn't seem to hold the smell like my down bags did, even over a week long trip.
-My synthetic stuff is not only for sleeping it. Im not afraid to take it out to glass with, sit by the fire with, or fish with. Ill break it out in the canoe and fish with it on. Sit on a hillside on the prairie to glass with or sit by the fire with it. Something I personally would not have done with my 400$ down bag.
I don't use synthetic because of some phobia of getting wet and being miserable. I just prefer synthetic all around for the reasons I listed above. While reading my comments keep in mind I have only used marmot down bags (lithium and hydrogen) and for synthetic Kifaru. The things outlined did not happen on backyard outings or in my head, they happened using the gear in the field. I don't have the experience some guys on here have, and some of them have likely been backpacking since before I was born, but that is the conclusion I have come up with from spending the last 4 years backpacking, hunting and fishing with my sleeping bags.
Let the down vs synthetic war begin
