Here's the short answer to Sonos Sub Gen 2 vs Gen 3:
While Sub Gen 3 is an upgrade over Sub Gen 2 in terms of processing speed, you don't need to spend extra for Gen 3 unless you're having wireless connectivity issues at home. Both models are virtually the same product.
...Meaning that they also perform the same in terms of sound quality.
Speaking of which...
Let me tell you something right off the bat.
The sound quality performance you'll end up getting from a speaker will always depend on your room acoustics - particularly room dimensions and speaker positions.
The impact of the combination of these two is actually so strong that in most cases, it doesn't even make sense to utter a single word on sound quality without speaking of them.
This is also why it's not unusual to see completely different reviews of the same speaker.
In one case the speaker might be placed in a sweet spot inside the room and hence the user might be satisfied. In other cases the same speaker might be ill placed and hence user might even have returned it.
The point most people miss here is that it mostly isn't even about the engineering behind the speaker itself. It's about where you place the speaker inside which room.
So, in order to solve this problem, I've partnered with Acoustics and Audio Engineering PhD Andrea Cicero from AC Acustica and created Soundton - a simple, 2D, browser accessible online speaker placement calculator.
With Soundton, now there's a way to figure the sound quality of most speakers before you buy them.
Read more about its working principles at soundton.com/documentation/.
The end colormap provides you the locations with the best (green) and worst (red) acoustics.