One is a streaming all-in-one and the other is an amplifier. Judge them on how many boxes you want and what you already own, not on the spec sheet alone.
| Area | Better | Why |
|---|
| Power | A | WiiM Amp Ultra 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. |
| Built-in DAC | evenly matched | Both have a DAC on board with much the same capability. |
| Streaming | A | Only WiiM Amp Ultra has Chromecast and Roon. |
| Phono stage | depends | Rotel A12 has a built-in phono stage (MM) and WiiM Amp Ultra does not. Decisive if you own a turntable, completely irrelevant if you do not - and an outboard phono stage is easy to add later either way. |
| Headphones | depends | Only Rotel A12 has a headphone output. Worth something if you listen late, nothing if you never do. |
| Amplifier class | depends | WiiM Amp Ultra is Class D and Rotel A12 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. |
| Shelf space | depends | WiiM Amp Ultra takes up about 68% less shelf area (522cm² against 1633cm²), and it is 119mm shallower, which is the measurement that decides whether a rack door shuts. |
| Price | A | WiiM Amp Ultra costs less - $549 against $800 at list. |
| Watts per dollar | A | WiiM Amp Ultra is the cheaper watt - about $5 per watt against $13. A blunt measure, and it says nothing about how either sounds, but it is the honest one for raw output. |
A WiiM Amp Ultra B Rotel A12
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?
WiiM Amp Ultra is the easier recommendation: it leads on most of the measured areas and costs less. Take Rotel A12 if one of the "depends" rows above describes your system. 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 - WiiM Amp Ultra 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. If you play records, Rotel A12 saves you buying a phono stage; if you do not, ignore that row entirely.
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.