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.)
A maximum of 50,000 bonus promo points can be earned on the 3XREWARD promotion code. Moosejaw Points are cut in half for sale items. So, if you get something on sale you'll actually get 15% back in points instead of 30% back. Promo Points cannot be earned on Gift Cards, Patagonia, Western Mountaineering, Montbell and Marmot. This promotional code can only be used once and is good through May 4, 2014. Your reward points won't show up in your account until after your order is shipped. See site for all program details.