In my opinion the Anker SoundCore 2 sounds better as the overal tone of the speaker is brighter. The SoundCore 3 has more bass but feels a bit muffled.

Anker SoundCore 2 can be connected as a stereo pair. You need two separate speakers for that.

Anker SoundCore 3 has the party cast option and you can connect up to 100 speakers to create the party experience. This would be 100 mono channels I suspect.