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 | B | Marantz Cinema 30 takes more analogue sources - 6 against 3. |
| Phono stage | depends | Marantz Cinema 30 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 Marantz Cinema 30 offers preamp outputs - which decides whether you can add a subwoofer or a power amplifier later without replacing the box. |
| Built-in sources | depends | Marantz Cinema 30 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 | B | Marantz Cinema 30 costs less - $4,800 against $5,500 at list. |
| Watts per dollar | B | Marantz Cinema 30 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 Marantz Cinema 30
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?
Marantz Cinema 30 is the easier recommendation: it leads on most of the measured areas and costs less. Take ARCAM AVA25 if one of the "depends" rows above describes your system. If you play records, Marantz Cinema 30 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.