Aside from the 1Shot guys who have obvious reasons for preferring the Stone Glacier, I'll be one of the first people to say I actually prefer the SG bags over FF and especially WM. I have had multiple WM and FF bags within the last 5 years and got rid of them all for the SG. Here are my worthless opinions on the bags I have had that I think are most comparable:
WM Badger: Great construction quality as always with WM, easily running zipper one-handed, prefer the feel of the Microfiber over their Extremlite nylons. But I honestly didn't like the hood design, I just struggled to get it to be uniformly tight when I needed to keep cold drafts out.
FF Swift YF 20: Same great construction as the Badger, better hood design, IMO. I prefer the Pertex YF fabric to any of WM's offerings, easily operated zipper. But for me, the deal-breaker was lack of a draft collar. For >20-degree bags in warmer weather, a draft collar isn't really necessary but once the temps drop below 20, I really want a draft collar
SG Chilkoot 15: Uses the Pertex YF fabric I prefer, I'm 6'1", 190 so the cut is about perfect for me, the magnetic draft collar is easy to operate in the dark and snaps together with magnets, I'm a very warm sleeper so I can run this bag any time of the year in the lower 48. Cons: Its made overseas, I personally think treated down is a joke and we're kidding ourselves to think it makes any real-world difference compared to high quality non-treated down. If you're that worried about wetting out the bag, just get a synthetic.