Both are NAD, from different ranges - the engineering approach is shared and the differences are mostly in power, connectivity and price.
| Area | Better | Why |
|---|
| Power | B | NAD C 328 has more power - 40W against 30W into 8 ohms. That is about 1.2dB, which is a small step in loudness but real headroom on peaks. |
| Noise floor | evenly matched | Much the same signal-to-noise ratio (98dB vs 100dB). |
| Built-in DAC | B | Both decode on board. NAD C 328 goes higher - 192kHz against 96kHz. Very few recordings exist above 192kHz, so treat this as headroom, not as sound quality. |
| Analogue inputs | B | NAD C 328 takes more analogue sources - 2 against 1. |
| Room to grow | evenly matched | The same expansion options on both. |
| Shelf space | depends | NAD D 3020 V2 takes up about 89% less shelf area (146cm² against 1349cm²), and it is 62mm shallower, which is the measurement that decides whether a rack door shuts. |
| Price | A | NAD D 3020 V2 costs less - $499 against $699 at list. |
A NAD D 3020 V2 B NAD C 328
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?
The usual trade-off: NAD C 328 measures better, NAD D 3020 V2 costs about 29% less. With most speakers in most rooms that gap is smaller in practice than it looks here. Think about the whole system: the roughly $200 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.