No single best speaker here - they are built to different priorities, and the right one depends on your room, your sources and what you listen to.
| Area | Better | Why |
|---|
| Connections | A | KEF LSX II adds Bluetooth, HDMI and digital inputs. |
| Size | depends | KEF LSX II is easier to place; Sonos Five is bigger, which usually goes with fuller bass. Your room decides. |
| Expandability | depends | KEF LSX II: a sub output; Sonos Five: a sub output. |
| Price | B | Sonos Five is cheaper - $1,098 against $1,500, about 27% less. |
A KEF LSX II B Sonos Five
depends neither is better in the abstract - it turns on your room, your system or how you will use them. Only specs published for both speakers are judged; anything missing on either side is left out rather than guessed.
Which should you choose?
KEF LSX II is ahead, but only on 1 of the measured areas, and it costs about 37% more. That is a lot of money for a narrow margin on paper - Sonos Five looks like the sensible buy unless something else about the KEF LSX II appeals to you. In a large or open-plan room, Sonos Five has the cabinet volume to fill it more easily; in a small room, near a wall or at desk distance, KEF LSX II is the easier speaker to get right. Think about the whole system, not just the speakers: the roughly $402 saved by taking the cheaper pair would buy a subwoofer or a better amplifier, and either usually does more for the sound than the difference between these two.
And remember what a spec sheet cannot show: how each looks in your room and whether the finish suits it, what dealer support and warranty are like where you live, and how they actually sound to you. If you can hear them first - ideally with your own music - that will tell you more than any number above.