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 | B | Polk XT15 digs deeper - 48Hz against 51Hz. A subwoofer would even that out. |
| What you buy | depends | DALI Oberon On wall C is a complete system - just add a source. Polk XT15 also needs an amplifier: more money and another box, but you choose it. |
| Connections | depends | With Polk XT15 that all comes from the amplifier you pair it with. |
| Upgrade path | depends | Polk XT15 can be re-amped later and outlive several amplifiers; DALI Oberon On wall C ages as one unit. |
| Size | depends | Polk XT15 is easier to place; DALI Oberon On wall C is bigger, which usually goes with fuller bass. Your room decides. |
| Price | B | Polk XT15 is cheaper - $199 against $1,249, about 84% less; arguably a different class. Speakers only - an amplifier narrows that gap. |
A DALI Oberon On wall C B Polk XT15
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?
DALI Oberon On wall C suits you if you want one box, ready to play, with nothing else to buy. Polk XT15 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. Think about the whole system, not just the speakers: the roughly $1,050 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.