According to Peter Pee on Youtube (great channel BTW, very informative on Sonos products), the Gen 2 has a slightly flatter response (Better for music) and the Gen 3 is slightly more biased to the lower bass frequencies (better for movies).

Additionally, Gen 3 frequency crossover is smoother, meaning it will be more difficult to localize the sub when watching shows (this is a good thing. You want the illusion that you cannot tell where the bass notes are coming from).

Future support, we can guess that Gen 3 may eventually get features that the Gen 2 is incapable of since Gen 3 has upgraded hardware. When this may happen is anyone’s guess at this point.

Basically, the above mentioned differences are very slight as early videos by Peter Pee he mentions he could not tell any audible difference between the 2 generations. His conclusions above was only after much more vigorous testing.

Basically it boils down to music or movies, peace of mind for future support and of course price. His videos are worth checking out if you still can’t decide.