Siblings in Polk Audio's Monitor XT series, so they share a family sound. It comes down to size, output and price.
| Area | Better | Why |
|---|
| Bass | A | Polk XT20 digs deeper - 38Hz against 94Hz. |
| Amplifier needs | B | Polk Audio Monitor XT90 is more sensitive (89dB vs 87dB), so it goes louder on the same amplifier. |
| Size | depends | Polk Audio Monitor XT90 is easier to place; Polk XT20 is bigger, which usually goes with fuller bass. Your room decides. |
| Type | depends | A Passive Bookshelf against a Passive Surround - a different job rather than a better one. |
| Price | B | Polk Audio Monitor XT90 is cheaper - $119 against $299, about 60% less; arguably a different class. |
A Polk XT20 B Polk Audio Monitor XT90
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?
Neither runs away with it - they trade advantages. Let the "depends" rows and your own room settle it. If a subwoofer is in your plans, the bass gap largely stops mattering - you would be crossing over above 94Hz anyway, which makes the cheaper Polk Audio Monitor XT90 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, Polk Audio Monitor XT90 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.