With so many options on the market, it can be confusing choosing what's best for your desired use. Here are some tips for making an informed choice!
First, is down right for you?
It used to be that down was the be-all, end-all for any serious winter pursuit. But in recent years, synthetic down has come a long way. Down is still the lighter and more compressible option, but many down jackets will - unless they've been specially treated - lose their "loft," or fluffiness factor, the moment they get wet.
Hydrophobic down, or down that has been treated to withstand moisture, is a new development on the market that's still a bit untested. Traditional down definitely has time on its side.
When it comes to choosing between down and synthetic, consider if getting soaked is possible or likely. If it is, you may be better off with a synthetic jacket, which will be heavier but will also retain much of its warming power when wet. Kayakers take note!
One last note on synthetic vs. down: down will generally last much longer than synthetic, hence its higher price tag. It's not unheard of for a high quality down jacket to be used for a decade or more, while a synthetic one will likely lose its ability to keep you warm by year five or six.
For the trail runner
If you're a trail runner, you know that it's really easy to go from overheated to chilled in a flash. You also probably value having as little as possible to carry. For that reason, a jacket with the label "ultralight" is your best bet. These jackets, often called down "sweaters," pack up to the size of your fist when not in use, and usually weigh much less than a pound. They're made of high-fill down (usually 800 or up) and won't keep you warm in a blizzard, but will definitely fight off the chill as you take in a view, and can then be packed away easily as you fly down the trail to your next destination.
For the backpacker
Consider a more mid-level warmth down jacket if backpacking is your sport of choice, but also keep a keen eye on weight, as every ounce counts. A higher fill (750 or up) is a smarter choice, as it will offer more warmth for less weight. Waterproofing on the outer shell likely isn't necessary, as you'll have a waterproof layer in your pack for that, but do pay attention to durability - a snag on a tree branch could leave you trailing white feathers for days. Some jackets have extra-thick patches on the shoulders and elbows for just this reason (and to shed water). Breathability is also more important than wind resistance here - you want a jacket that will breathe as your temperature fluctuates on uphills and downhills.
For the sport climber or boulderer
If you're hoping to send your next project while the friction is ideal, you're probably getting out on the rock in the next few months as temperatures drop. And if you're a good partner, you're probably going to be catching quite a few falls as your friend works on their project, too. For that reason, go for the warmest option you can afford. The higher the fill, the better, and worry less about weight - it's more important that you are able to stay warm while not moving in between send attempts. For this reason, a hood is a must! Think "parka."
A good down jacket is a must-have tool in any outdoorsman or woman's arsenal. Having a few with a variety of fills and warmth levels is great, but if budget is a concern, aim for the right jacket for your sport of choice.