Amazon Echo, Google Home or Sonos One: which smart speaker should I buy?

Smart speakers are set to be the hottest Christmas gift this year. On Black Friday, Amazon dropped the price of its core Echo product to £79 (it is back up to £90 now), while Google slashed the cost of its Home device from £129 to £77.50 at most outlets (it is also back up now). Meanwhile, Apple is promising to launch its version, HomePod, although the price point is rumoured to be significantly higher.