I voted for Roxie, Burgh, and Elesa, which happen to be consecutive gyms.
Roxie was great addition! We have never had an alternative chick as a gym leader. I love the vibe of the city as well. It is not overdone, yet still has a grungy seaport charm, in which Roxie is able to complement.
Burgh is apparently not liked by anyone else, haha. I liked his honeycomb gym, but the cacoon gym too it to a whole new level of whimsical, in addition to the colorful paint room in which you encounter Burgh. Plus, I love bug pokemon.
Elesa, do I even need to say anything? Tall, blonde, composed, model, that specializes in electric types. Well, actually, she had jet black hair in BW2 which was probably the most fresh revamp from the previous version, along with her plush Mareep-fur coat, and head phones that resembled pointed ears.