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 | B | Arcam A25+ has more power - 100W against 72W into 8 ohms. That is about 1.4dB, which is a small step in loudness but real headroom on peaks. |
| Built-in DAC | B | Both decode on board. Arcam A25+ goes higher - 384kHz against 192kHz. Very few recordings exist above 192kHz, so treat this as headroom, not as sound quality. |
| Analogue inputs | A | Rega Elex Mk4 takes more analogue sources - 5 against 3. |
| Use with a TV | depends | Only Arcam A25+ has HDMI eARC, so the television can drive it directly and one remote controls the volume. If the system is for music only, this changes nothing. |
| Room to grow | evenly matched | The same expansion options on both. |
| Amplifier class | depends | Rega Elex Mk4 is Class A/B and Arcam A25+ is Class G. Class A/B runs warm and is the long-established mainstream choice; Class G/H switches its supply rails to cut the heat a Class A/B design wastes. Modern examples of both measure well - judge by the rest of the page. |
| Price | A | Rega Elex Mk4 costs less - $1,895 against $2,000 at list. |
| Watts per dollar | B | Arcam A25+ is the cheaper watt - about $20 per watt against $26. A blunt measure, and it says nothing about how either sounds, but it is the honest one for raw output. |
A Rega Elex Mk4 B Arcam A25+
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?
The usual trade-off: Arcam A25+ measures better, Rega Elex Mk4 costs about 5% less. With most speakers in most rooms that gap is smaller in practice than it looks here. If this sits under a television, Arcam A25+ is the one to buy - HDMI ARC means the TV remote controls the volume and there is no second box in the way.
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.