If you need greater bandwidth and use Apple's AirPlay 2, choose Sonos Gen 2. Otherwise, Sonos Gen 1 is fine. Regarding the speaker itself, both models have identical audio quality.
Unlike some Sonos speakers, One is a smart speaker that integrates virtual assistants like Google Assistant and Amazon Alexa.
Both One Gen 1 and Gen 2 are the same speakers. The differences between the two?
The latter has greater memory and a faster processor. Also, Gen 2 comes with Bluetooth Low Energy (BLE) to facilitate the initial setup of the speaker, allowing a quick and convenient (and temporary) interface between Gen 2 and the provisioning mobile device.
Sonos discontinued Gen 1 upon the release of Gen 2 in March 2019 but both models are supported.
If you need greater bandwidth and use Apple's AirPlay 2, choose One Gen 2. Otherwise, Gen 1 is fine.
In summary, if you're an iOS devotee, choose Gen 2. Android, PC and Mac users can suffice with Gen 1.Those who place a heavy load on One (using the virtual assistant, streaming music from multiple services, podcasts) may have peace of mind by going with Gen 2.
Sound Quality
ASAP Science made a video on the loudest and quietest rooms in the world. A mind blowing example of the importance of acoustics (time adjusted video).
Other parameters such as the age/materials of the building, the furniture & carpets in place, ceiling height, etc can and will, of course, have an effect on room acoustics, too. But much less.
Anyways...
Sonos One is the company's "entry-level" speaker. But unless you're an audiophile, you'll likely not discern any sonic differences between One and Sonos' premium models, like Five.
Sonos One delivers rich, full bass from a dedicated mid-woofer with a clear definition from mid-range sounds. It also has a tweeter and six far-field mics, all powered by two Class-D amplifiers.
You'll hear impressive sound intricacy from recorded musical instruments, like discrete glissando from a piano and portamento from a slide guitar. With vocals, there's no quality change in the overall sound when the instruments move further back in the mix.
Users also have the option of connecting One with other Sonos speakers (like Soundbar, Playbar or Arc) for immersive home theater surround sound.
Most people will have no issue with the loudness of Sonos One. Its sound will fill any mid-size room like a den, bedroom or study.
Also, you won't need to shout at the speaker when you're engaging with Alexa or Google Assistant.
However, we should mention that pcmag.com carps that Sonos One's "sound can distort at high volumes" and zdnet.com found that One's "bass output was a bit weaker" than expected.
Here is the user guide for Sonos One.
In my opinion, Sonos One (see image) blends in well with most concepts.
Loudness & Power
Specifically, Sonos One pumps out 65 dB, which according to diysmarthings.com is the equivalent of 90 kW. For those unaware, 65 dB is the level of sound generated during a normal conversation or by laughter.
Sonos One uses an auto-switchable 100 - 240 VAC, 50/60 Hz power supply. To prevent corrupting the WiFi signal feeding One, Sonos warns against placing the speaker on metal, concrete, brick or marble.
Features
Sonos One connects any 2.4 GHz WiFi network using an 802.11b/g router. Note that 5 GHz networks (802.11n/ac/ax) are incompatible with the speaker. One also comes with a 10/100 Mbps Ethernet port.
While the Sonos controller app serves as a remote control for One, the speaker features basic top panel controls for sound volume, play/pause, next/previous track and microphone/voice assistant mute.
The top panel also has LEDs showing status and microphone indicators. Both Gen 1 and Gen 2 can be managed using either the S1 and S2 app.
All Sonos speakers are Apple-friendly, and One is no exception. While the Sonos controller app can be downloaded for Android, one needs iOS to take full advantage of all of One's features.
For example, Sonos Trueplay—which fine-tunes the speaker's sound to the unique acoustical environment of your listening area—can only be used with iOS 7 or later versions.
While Sonos Gen 2 touts an improved processor and updated memory compared to Gen 1, this upgrade addresses "future-proofing" Gen 2 if and when Sonos upgrades the speaker's firmware.
As noted above, we recommend using Sonos Gen 2 to prevent any Apple Airplay 2 snafus. Gearpatrol.com suspects that Gen 2's raison d'etre is due to Airplay 2, as some users reported difficulties using Airplay 2 with Gen 1.
As with other Sonos speakers, One supports multi-room music playback with the controller app. Use the app with dozens of streaming music services and music files stored on a network-attached storage (NAS) device (including smartphone, tablet or laptop/desktop computer).
Note that the listener wants stereo sound from One, it must be paired with another Sonos speaker (other than Play or Move).
Sonos One measures 6.4 in x 4.7 in x 4.7 in (16.15 cm x 12 cm x 12 cm) and is available in either white with a white matte grille or black with a black matte grille.
Looks
Sonos One measures 6.4 in x 4.7 in x 4.7 in (16.15 cm x 12 cm x 12 cm) and is available in either white with a white matte grille or black with a black matte grille. The speaker weighs 4 lbs (1.85 kg).
The Verdict
If you're an iOS devotee, choose Sonos Gen 2. Android, PC and Mac users can suffice with Gen 1. If cost is an issue, you can save a few bucks by opting for Gen 1. Those who place a heavy load on One (using the virtual assistant, streaming music from multiple services, podcasts) may have peace of mind by going with Gen 2.
Some individual video reviews of the two: