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 A15 has more power - 80W against 50W into 8 ohms. That is about 2dB, so it plays usefully louder before it runs out and has more in hand on peaks. |
| Room size | depends | We rate Arcam A15 the better fit for a mid-size room, a large room and a very large room, and Rotel A11 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. |
| Speaker load rating | A | Arcam A15 is rated down to 4 ohms against 8, so it is the safer partner for a low-impedance speaker. |
| Noise floor | A | Arcam A15 is the quieter design on paper - 106dB against 90dB. 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 A11 MKII takes more analogue sources - 4 against 3. |
| Room to grow | A | Only Arcam A15 offers preamp outputs - which decides whether you can add a subwoofer or a power amplifier later without replacing the box. |
| Price | B | Rotel A11 MKII costs less - $799 against $999 at list. |
| Watts per dollar | A | Arcam A15 is the cheaper watt - about $12 per watt against $16. A blunt measure, and it says nothing about how either sounds, but it is the honest one for raw output. |
A Arcam A15 B Rotel A11 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 A15 leads across most of the measured areas for a fairly modest premium, so it is the easier pick if the budget stretches. Rotel A11 MKII is the one to take if it does not. 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 A15 has the headroom, and headroom is what stops an amplifier hardening up on peaks. At desk distance or in a small room, 50 watts is already more than most people ever use, and the extra 30 watts would be headroom you pay for and never hear - we rate Arcam A15 poorly for near-field use for exactly that reason.
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.