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 | B | NAD C 388 has more power - 150W against 100W into 8 ohms. That is about 1.8dB, which is a small step in loudness but real headroom on peaks. |
| Room size | depends | We rate Arcam A25 the better fit for desk or near-field listening, a small room and a mid-size room, and NAD C 388 for a very large room. Match the amplifier to the room you actually have, not the one you want. |
| Grip on hard loads | A | Arcam A25 holds up better into a 4-ohm load: its output increases strongly to 165W, where the other barely increases. That matters with demanding speakers far more than the 8-ohm figure does. |
| Noise floor | A | Arcam A25 is the quieter design on paper - 106dB against 95dB. 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. |
| Analogue inputs | A | Arcam A25 takes more analogue sources - 3 against 2. |
| Room to grow | evenly matched | The same expansion options on both. |
| Amplifier class | depends | Arcam A25 is Class G and NAD C 388 is Class D. Class G/H switches its supply rails to cut the heat a Class A/B design wastes; 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 | Arcam A25 takes up about 14% less shelf area (1580cm² against 1840cm²), and it is 59mm shallower, which is the measurement that decides whether a rack door shuts. |
| Price | evenly matched | Priced within a few per cent of each other. |
| Watts per dollar | B | NAD C 388 is the cheaper watt - about $10 per watt against $15. A blunt measure, and it says nothing about how either sounds, but it is the honest one for raw output. |
A Arcam A25 B NAD C 388
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?
Arcam A25 has the edge on paper, though not by much. The rows marked "depends" are more likely to decide this than the score is. If your speakers are a difficult load - 4 ohms nominal, big woofers, or a sensitivity in the low 80s - Arcam A25 is the safer partner, because how an amplifier behaves when the impedance drops matters more than its 8-ohm rating.
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.