Surprisingly many votes for the Roxie battle, I usually see a lot of hate for that battle, but I guess still many people like it. I'm indifferent on that one myself.
My favourite battle would be Ash vs. Brycen. Not a very spectacular or memorable gym battle, but it had some cool things. Pignite coming into action not too long after its evolution, showing off his awesome new move Fire Pledge, Scraggy getting battletime and doing good in battle, and finally Krokorok also getting battletime and being able to overcome the type-disadvantage to defeat Brycen's strong Beartic.