Fortree City gym, hands down. I wasn't too crazy about Pikachu vs. Pelipper (boring much?), but the other two battles were fantastic. Grovyle's agility and Swellow's aerial adventures is a combination that doesn't fail to impress, and coupled with the stylised artwork that made all the attacks look really intense...well, it's obvious you have a winner on your hands.
As for Contests, Fallabour (how do you spell it kids!) town was easily the best in terms of battling. The first time Haruka managed to show that she could think up a great strategy on the spot, with some excellent move combinations from two decent pokémon. And of course, kickass animation.
...Lilycove comes in a close second however! Huzzah for white meat.