I'm a 6 foot tall, slim build guy. I weigh 150lbs. 15-neck and a 33-arm.I ordered the small and medium. I am keeping the medium and returning the small. The medium fits just right. I hope my numbers help you make your choice.
I purchased the Ajax because I had a marmot shell that was zip-in compatible and the AJAX fit the bill. I have had it in -15F weather with a windchill of -34F and I will tell you I wasn't cold, which is saying something for that kind of temperature. Overall for a sub $175 jacket, this thing is pretty sweet. I would recommend getting one.
"Good Entry-Level Down Jacket, Has some Issues"
Firstly, I am 5'9" and 175 pounds, and am usually a medium all-around. This jacket fits larger than most, and I could probably size down to a small. It is a great jacket for the money, especially if you are looking for an entry-level down jacket. Good and light, and very warm. I like the chest pocket, but I am not highly impressed by the build of the shoulders. It is very boxy, and was probably intended to make it look urban and stylish. In my experience it makes you look oddly boxy and broad, or like you have on shoulder pads. Someone with broader shoulders would probably fill it out and look like a million bucks, but for me it creates some air space in the upper chest area that is a little chilly. I will stick to my other down jacket for backcountry pursuits, but if you want a smart-looking jacket to wear on the weekend, this might be it for you! (Just make sure the sizing is right on you, you may have to size down.)
96 hour sale prices are only good on in-stock items and cannot be applied to prior purchases or combined with other promotions. Not all items from selected brands will be on clearance. Sale includes discontinued and prior season styles and colors from select brands. The code excludes GoPro, Snow/Wake/Skate brands, including Burton, Volcom, Liquid Force, Foursquare, Analog, Sessions, Oakley and others. Exclusions apply. Prices are while supplies last and are subject to change. Sale ends March 9, 2014 at 11:59pm EDT.