No single best amplifier here. What decides it is what you have to drive, what you need to plug in, and how much of the system you want in one box.
| Area | Better | Why |
|---|
| Power | evenly matched | Effectively the same output - 30W against 30W into 8 ohms is under 1dB, which is not an audible difference in loudness. |
| Noise floor | A | Onkyo A-9110 is the quieter design on paper - 103dB against 98dB. Audible mainly with sensitive speakers in a quiet room. |
| Built-in DAC | B | NAD D 3020 V2 has a DAC on board; the other needs an external one, which is another box, another power lead and another purchase. |
| Amplifier class | depends | Onkyo A-9110 is Class A/B and NAD D 3020 V2 is Class D. Class A/B runs warm and is the long-established mainstream choice; Class D runs cool and draws almost nothing at idle. Modern examples of both measure well - judge by the rest of the page. |
| Shelf space | depends | NAD D 3020 V2 takes up about 90% less shelf area (146cm² against 1434cm²), and it is 82mm shallower, which is the measurement that decides whether a rack door shuts. |
| Price | A | Onkyo A-9110 costs less - $349 against $499 at list. |
| Watts per dollar | A | Onkyo A-9110 is the cheaper watt - about $12 per watt against $17. A blunt measure, and it says nothing about how either sounds, but it is the honest one for raw output. |
A Onkyo A-9110 B NAD D 3020 V2
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 amplifiers are judged; anything missing on either side is left out rather than guessed.
Which should you choose?
Onkyo A-9110 has the edge on paper, though not by much. The rows marked "depends" are more likely to decide this than the score is. If you already own a DAC or a streamer, the built-in one is money you are paying twice for, and Onkyo A-9110 becomes the more rational buy. Think about the whole system: the roughly $150 saved by taking the cheaper one would buy better speakers or a subwoofer, which does more for the sound than the difference between two competent amplifiers.
What a spec sheet cannot show: how either sounds with your speakers, how the controls feel day to day, and what the app is like to live with - which is where most all-in-one amplifiers are actually won or lost. Power figures are the manufacturers' own and are not measured to a common standard, so treat small differences as noise. If you can hear both, that will tell you more than any row above.