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 - 120W against 145W into 8 ohms is under 1dB, which is not an audible difference in loudness. |
| Speaker load rating | B | ARCAM AVA35 is rated down to 4 ohms against 8, so it is the safer partner for a low-impedance speaker. |
| Analogue inputs | A | ARCAM AVR31 takes more analogue sources - 6 against 3. |
| Room to grow | A | Only ARCAM AVR31 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 AVR31 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 | evenly matched | Priced within a few per cent of each other. |
A ARCAM AVR31 B ARCAM AVA35
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 AVR31 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.