TL;DR. Two airline cobrands for different coastlines. United Quest ($350) is for United-heavy flyers (mostly Midwest, East Coast hubs ORD, EWR, IAD). Atmos Ascent ($95) is for Alaska-heavy flyers (West Coast, Hawaii, Alaska). Different airlines, different hubs, different cards. The decision is "which airline do you actually fly," not which card is better.
The three dimensions that actually decide it. First, hub geography. If you fly out of ORD, EWR, DEN, SFO (United hubs), Quest. If you fly out of SEA, LAX, PDX, ANC, HNL (Alaska hubs), Atmos. Second, fee. $255 difference. Atmos is significantly cheaper. Third, companion certificate vs travel credit. Atmos has the Companion Fare ($99 plus taxes, book once a year). Quest has $125 in travel credit and free bags.
Real customer scenario for each. If you live in Seattle and fly Alaska 3+ times a year, Atmos is correct. If instead you live in Newark and fly United, Quest is correct. There is essentially no overlap in optimal use.
The trap to avoid. Holding both because "diversification." Airline cobrand cards lock in to their specific carrier. If you fly two airlines, hold the cobrand of the one you fly more, and use a transferable points card (CSP, Venture X, Amex Gold) for the other.