Different kinds of product: one is active with its amplifier built in, the other passive and needs one. Judge them on how you want to own the system, not just the specs.
| Area | Better | Why |
|---|
| Bass | A | KEF Coda W digs deeper - 41Hz against 51Hz. |
| What you buy | depends | KEF Coda W is a complete system - just add a source. KEF Q150 also needs an amplifier: more money and another box, but you choose it. |
| Connections | depends | KEF Coda W has Bluetooth and HDMI built in. With KEF Q150 that all comes from the amplifier you pair it with. |
| Upgrade path | depends | KEF Q150 can be re-amped later and outlive several amplifiers; KEF Coda W ages as one unit. |
| Size | depends | Similar cabinet size - neither is easier to fit. |
| Expandability | A | KEF Coda W: a sub output. |
| Price | B | KEF Q150 is cheaper - $600 against $999, about 40% less; arguably a different class. Speakers only - an amplifier narrows that gap. |
A KEF Coda W B KEF Q150
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 Coda W suits you if you want one box, ready to play, with nothing else to buy. KEF Q150 suits you if you already have an amplifier, want to choose the electronics, or expect to upgrade in stages. Neither is the better speaker in the abstract. If a subwoofer is in your plans, the bass gap largely stops mattering - you would be crossing over above 51Hz anyway, which makes the cheaper KEF Q150 much easier to justify. Think about the whole system, not just the speakers: the roughly $399 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.