A floor-standing against a bookshelf. They are built for different places in a room, so start with where these have to go rather than which looks better on paper.
| Area | Better | Why |
|---|
| Bass | A | Q Acoustics M40 digs deeper - 38Hz against 55Hz. |
| Built-in power | B | Q Acoustics M20 HD has the bigger amplifier (128W vs 50W RMS). |
| Connections | evenly matched | The same set of inputs and streaming options. |
| Size | depends | Q Acoustics M20 HD is easier to place; Q Acoustics M40 is bigger, which usually goes with fuller bass. Your room decides. |
| Type | depends | A Powered Floor-standing against a Powered Bookshelf - a different job rather than a better one. |
| Expandability | depends | Q Acoustics M40: a sub output; Q Acoustics M20 HD: a sub output. |
| Price | B | Q Acoustics M20 HD is cheaper - $599 against $999, about 40% less; arguably a different class. |
A Q Acoustics M40 B Q Acoustics M20 HD
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 55Hz anyway, which makes the cheaper Q Acoustics M20 HD much easier to justify. In a large or open-plan room, Q Acoustics M40 has the cabinet volume to fill it more easily; in a small room, near a wall or at desk distance, Q Acoustics M20 HD 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.