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 XT20 digs deeper - 38Hz against 52Hz. |
| What you buy | depends | Edifier MR3 is a complete system - just add a source. Polk XT20 also needs an amplifier: more money and another box, but you choose it. |
| Connections | depends | Edifier MR3 has Bluetooth built in. With Polk XT20 that all comes from the amplifier you pair it with. |
| Upgrade path | depends | Polk XT20 can be re-amped later and outlive several amplifiers; Edifier MR3 ages as one unit. |
| Size | depends | Edifier MR3 is easier to place; Polk XT20 is bigger, which usually goes with fuller bass. Your room decides. |
| Expandability | depends | Neither adds bi-amping, a sub output or height drivers. Polk XT20 sits in a wider range (9 models), so a matched surround system is easier later. |
| Price | A | Edifier MR3 is cheaper - $150 against $299, about 50% less; arguably a different class. And that is the whole system. |
A Edifier MR3 B Polk XT20
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?
Edifier MR3 suits you if you want one box, ready to play, with nothing else to buy. Polk XT20 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 52Hz anyway, which makes the cheaper Edifier MR3 much easier to justify. In a large or open-plan room, Polk XT20 has the cabinet volume to fill it more easily; in a small room, near a wall or at desk distance, Edifier MR3 is the easier speaker to get right.
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.