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 - 50W against 60W into 8 ohms is under 1dB, which is not an audible difference in loudness. |
| Noise floor | B | Rotel A12 MKII is the quieter design on paper - 100dB against 90dB. Audible mainly with sensitive speakers in a quiet room. |
| Built-in DAC | evenly matched | Both have a DAC on board with much the same capability. |
| Room to grow | B | Only Rotel A12 MKII offers preamp outputs - which decides whether you can add a subwoofer or a power amplifier later without replacing the box. |
| Amplifier class | depends | NAD C3030 is Class D and Rotel A12 MKII is Class A/B. Class D runs cool and draws almost nothing at idle; Class A/B runs warm and is the long-established mainstream choice. Modern examples of both measure well - judge by the rest of the page. |
| Shelf space | depends | NAD C3030 takes up about 26% less shelf area (1208cm² against 1633cm²), and it is 40mm shallower, which is the measurement that decides whether a rack door shuts. |
| Price | B | Rotel A12 MKII costs less - $1,100 against $1,199 at list. |
| Watts per dollar | B | Rotel A12 MKII is the cheaper watt - about $18 per watt against $24. A blunt measure, and it says nothing about how either sounds, but it is the honest one for raw output. |
A NAD C3030 B Rotel A12 MKII
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?
Rotel A12 MKII has the edge on paper, though not by much. The rows marked "depends" are more likely to decide this than the score is.
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.