I've never been to Alaska so with that said...... I would lean toward a quilt. If you are only going to have one for all seasons I would go with a 0 degree quilt and a good quality pad. With the quilt you should be able to uncover/ self regulate when it's warm and with a good pad you should be plenty warm in the cold. Im not sure if it's available but I would want one with a zippered footbox. I would hate to have to tuck my feet into an enclosed footbox when it's warm. You could go with a little warmer rated quilt as well and wear wool base layers when it's really cold to add some warmth.
Depends on what your doing and when in Alaska. I have multiple bags, I used a 10-20 degree bag for moose and sheep. I am a cold sleeper though, then I hunt the north slope for caribou in Oct & Nov and I use a -20 bag with a fleece liner which puts it at about -30. AK summers in the interior can hit 80 degrees so you pretty much wouldn't need a bag. So is there a one and done bag for AK? I think you could get away with a 30 degree bag if your not doing anything later than say Sep. But you would be sweating in the summers!
I have not even tried a quilt so no way I can comment there. I am now looking at a new bag. Cannot believe I am but I am. So when i am in any bag if I am too warm I just un-zip a little and I am fine. My mindset is it would not be the same if it is too cold in a quilt? Maybe they are built better than what i suspect but a good bag gives me a sense of security, if it is not warm enough I add another layer.
Bob, if you want to check out a quilt let me know. I have a few of them, and I love them. I hate sleeping constricted in a cocoon, and can't stand a sleeping bag hood.
I have been through this very situation several times, due to space limits when working alone in remote wilderness, using my own gear and needing items that would double for hunting, camping (BC-12 months of the year) and even as bedding when in college.
I use both synthetic and down bags, do prefer a REALLY FINE down bag and have/do own most of the big names. At present, I would suggest either a Western Mountaineering Kodiak or a Valandre Shocking Blue and buy the WM in "microfiber", use a bivy if in really wet conditions.
That said, I actually have/do use two down bags for most things, a -20 model, mine is the fabulous ORIGINAL XPDII and it was custom made for me by Integral Designs of Calgary, AB. I have never seen/used a better bag in my 50+ years of use in northern and western Canada.
I sold my last light bag, an Alpinlight, by WM and will soon buy a WM Terralite to replace it, just due to more space. I like to have a 20-25*F down bag as well as the -20*F type and have done this for almost 40 years.....get the 0* to -20*F one if one is all you want or can afford and buy the BEST, it really pays off.