Siblings in Polk Audio's Signature Elite series, so they share a family sound. It comes down to size, output and price.
| Area | Better | Why |
|---|
| Bass | A | Polk ES20 digs deeper - 41Hz against 142Hz. |
| Amplifier needs | evenly matched | Similar sensitivity (86dB vs 85dB) - both want much the same power. |
| Size | depends | Polk Audio Signature Elite ES90 is easier to place; Polk ES20 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. |
| Cabinet | depends | Ported vs Sealed. Sealed is tighter and happier near a wall; ported digs lower but wants space behind it. |
| Price | evenly matched | Much the same money ($399 vs $405 a pair). |
A Polk ES20 B Polk Audio Signature Elite ES90
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?
Polk ES20 has the edge on paper, though the margin is not large. The rows marked "depends" may matter more to you than the score does. If a subwoofer is in your plans, the bass gap largely stops mattering - you would be crossing over above 142Hz anyway, so judge these on the other rows instead. In a large or open-plan room, Polk ES20 has the cabinet volume to fill it more easily; in a small room, near a wall or at desk distance, Polk Audio Signature Elite ES90 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.