What are you using it for? Wet or dry environment? In a tent or on the ground or in the snow? Are you willing to carry a liner and or cover (bivy sack) of any kind? Is compressibility important (does it need to pack small)? How is it shaped? How are you shaped? Can you tolerate a slim cut mummy bag or will you sleep better with a more generous cut for your hips, shoulders, etc? Car camping, rafting, desert backpacking, Alaska backpacking, mountaineering, hunting in the late fall above 5000 ft, through hiking the AT, multi-day adventure racing….all get their own sleep system considerations.
There are some great sleeping bags out there. Synthetic fill is bulkier for the same insulation than down. Every time you compress synthetic, it loses some loft and thus insulating ability. However, synthetic will stay warmer in wetter environments, over time, as everything gets wet.
Down compresses smaller and recovers better from compression. If you get down wet, it stops working. Improvements to waterproof fabrics make the moisture issue less of a concern than in the past but it’s a thing. Especially if you expect to get rained on for days in a row.
You can get away with less insulation if you use a liner. Likewise, a bivy sack. However, if the bivy sack is cut small and compresses the insulation, it can actually have the opposite effect.
What kind of pad are you carrying? That makes a difference too.
Good gear is expensive. You get what you pay for so decide what you need and pay for it. Western Mountaineering, Feathered Friends, Wiggins, Enlightened equipment, Warmlite, hell, even Wenzel is made in the USA. I have sleeping bags for high altitude mountaineering, for car camping, for summer backpacking and for team sleeping with my favorite naked friend. Each is different and specialized and was chosen for different reasons.