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 - 120W against 140W into 8 ohms is under 1dB, which is not an audible difference in loudness. |
| Analogue inputs | A | ARCAM AVA25 takes more analogue sources - 3 against 2. |
| Phono stage | depends | NAD T 778 has a built-in phono stage and ARCAM AVA25 does not. Decisive if you own a turntable, completely irrelevant if you do not - and an outboard phono stage is easy to add later either way. |
| Room to grow | B | Only NAD T 778 offers preamp outputs - which decides whether you can add a subwoofer or a power amplifier later without replacing the box. |
| Amplifier class | depends | ARCAM AVA25 is AB and NAD T 778 is 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. |
| Price | B | NAD T 778 costs less - $4,799 against $5,500 at list. |
| Watts per dollar | B | NAD T 778 is the cheaper watt - about $34 per watt against $46. A blunt measure, and it says nothing about how either sounds, but it is the honest one for raw output. |
A ARCAM AVA25 B NAD T 778
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?
NAD T 778 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 play records, NAD T 778 saves you buying a phono stage; if you do not, ignore that row entirely.
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.