Bose - QuietComfort Ultra Headphones vs Sennheiser - HD 660S2

These two are nearly even on the Mars Score (62.9 vs 64.2). The decision isn't about overall quality — both clear the bar — it's about which specific trade-offs fit your use.

Pick the QuietComfort Ultra Headphones if you carry the device everywhere and weight or thickness has been the deciding factor before. The biggest gaps in its favor are weight, active noise cancellation, spatial audio, among others.

Pick the HD 660S2 if you care most about driver size. Its strongest claims are driver size.

Both ship with comparable ldac, water resistance, so those specs don't separate the two — focus on the differences below.

Bottom line: there is no wrong answer here — match the spec advantages to how you actually use the product. The Mars Score parity tells you both are well-rounded; the differences are about trade-offs, not quality.