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 - 60W against 50W into 8 ohms is under 1dB, which is not an audible difference in loudness. |
| Noise floor | B | Arcam A5+ 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 | A | Rotel A12 takes more analogue sources - 4 against 3. |
| Room to grow | evenly matched | The same expansion options on both. |
| Price | A | Rotel A12 costs less - $800 against $1,200 at list. |
| Watts per dollar | A | Rotel A12 is the cheaper watt - about $13 per watt against $24. A blunt measure, and it says nothing about how either sounds, but it is the honest one for raw output. |
A Rotel A12 B Arcam A5+
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?
Rotel A12 has the edge on paper, though not by much. The rows marked "depends" are more likely to decide this than the score is. Think about the whole system: the roughly $400 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.