Two versions of the same amplifier rather than two different designs, so the question is not which is better built but which set of features you actually need - and what the difference costs.
| Area | Better | Why |
|---|
| Power | evenly matched | Effectively the same output - 110W against 120W into 8 ohms is under 1dB, which is not an audible difference in loudness. |
| Speaker load rating | B | ARCAM AVA25 is rated down to 4 ohms against 8, so it is the safer partner for a low-impedance speaker. |
| Analogue inputs | A | ARCAM AVR21 takes more analogue sources - 6 against 3. |
| Room to grow | A | Only ARCAM AVR21 offers preamp outputs - which decides whether you can add a subwoofer or a power amplifier later without replacing the box. |
| Built-in sources | depends | ARCAM AVR21 has a radio tuner built in. That is one less box if you still play discs or listen to radio, and dead weight if you do not. |
| Price | A | ARCAM AVR21 costs less - $4,700 against $5,500 at list. |
A ARCAM AVR21 B ARCAM AVA25
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 AVR21 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.