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 - 90W against 100W into 8 ohms is under 1dB, which is not an audible difference in loudness. |
| Built-in DAC | A | FiiO AIR AMP has a DAC on board; the other needs an external one, which is another box, another power lead and another purchase. |
| Analogue inputs | B | Yamaha R-S202 takes more analogue sources - 4 against 1. |
| Room to grow | A | Only FiiO AIR AMP offers preamp outputs and a subwoofer output - which decides whether you can add a subwoofer or a power amplifier later without replacing the box. |
| Amplifier class | depends | FiiO AIR AMP is Class D and Yamaha R-S202 is Class A/B. Class D runs cool and draws almost nothing at idle; 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 | Yamaha R-S202 costs less - $250 against $300 at list. |
| Watts per dollar | B | Yamaha R-S202 is the cheaper watt - about $3 per watt against $3. A blunt measure, and it says nothing about how either sounds, but it is the honest one for raw output. |
A FiiO AIR AMP B Yamaha R-S202
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?
Neither runs away with it - they trade advantages. Let the "depends" rows and the speakers you already own settle it. If you already own a DAC or a streamer, the built-in one is money you are paying twice for, and Yamaha R-S202 becomes the more rational buy.
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.