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 | A | Arcam A25 has more power - 100W against 60W into 8 ohms. That is about 2.2dB, so it plays usefully louder before it runs out and has more in hand on peaks. |
| Room size | depends | We rate Arcam A25 the better fit for a mid-size room, a large room and a very large room, and Rotel A12 MKII for desk or near-field listening and a small room. Match the amplifier to the room you actually have, not the one you want. |
| Noise floor | A | Arcam A25 is the quieter design on paper - 106dB against 100dB. 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 | B | Rotel A12 MKII takes more analogue sources - 4 against 3. |
| Room to grow | evenly matched | The same expansion options on both. |
| Amplifier class | depends | Arcam A25 is Class G and Rotel A12 MKII is Class A/B. Class G/H switches its supply rails to cut the heat a Class A/B design wastes; Class A/B runs warm and is the long-established mainstream choice. Modern examples of both measure well - judge by the rest of the page. |
| Price | B | Rotel A12 MKII costs less - $1,100 against $1,499 at list. |
A Arcam A25 B Rotel A12 MKII
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 is ahead, but on only 1 of the measured areas, and it costs about 36% more. That is a lot of money for a narrow margin - Rotel A12 MKII is the sensible buy unless a specific feature above decides it for you. Start with the room. In a large or open-plan room, or with speakers that are hard to drive - low sensitivity, or an impedance that dips - Arcam A25 has the headroom, and headroom is what stops an amplifier hardening up on peaks. At desk distance or in a small room, 60 watts is already more than most people ever use, and the extra 40 watts would be headroom you pay for and never hear - we rate Arcam A25 poorly for near-field use for exactly that reason. Think about the whole system: the roughly $399 saved by taking the cheaper one would buy better speakers or a subwoofer, which does more for the sound than the difference between two competent amplifiers.
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.