I've used both down and synthetic and even though synthetic weighs more I prefer synthetic. Down bags lose their loft and are hard to clean, the feathers soak up body oils and start packing down instead of lofting. My thirty below zero bag developed a lot of empty spots where there wasn't anything between me and the outside but two layers of ripstop nylon. The feathers were still there but were all in one small spot. I know there are some products out there which are supposed to clean down bags without destroying the loft but I don't believe in them. Anything strong enough to remove the stuff that's left behind when your hiking dog finds somebody's toilet and rolls in it, and then thinks it's a wonderful idea to go back to camp and take a nap on your nice goosedown bag, is enough to ruin the bag just from the cleaning process. That's the kind of problem you can run into no matter what bag you use. Synthetics clean up better. My synthetic bag isn't as warm as my goosedown bag was when it was new, but it has lasted a lot longer and I've been able to clean it without ruining it. So I think synthetic is a right decision, unless you're rich enough to treat goosedown as a disposable item. Synthetics keep their loft even if they're wet, so you don't lose all the insulation value if the bag gets soaked. Goosedown's useless in that circumstance. I wouldn't buy another one even though I remember it as the only thing that could keep me warm when I got back from Vietnam.

JimmyTH