VI was way better imo.
I love VII, but VI had waaayy better music, and better graphics (VII felt like I was watching the music video for that song about moving refrigerators and color T.V's).
I liked the world and atmosphere of VI much better than VII's. The latter's world was too ugly for me. Why explore dirty sewers in a video game when I have to do that everyday in real life?
Also, the story and characters of VI ruled, as well as the Esper system. VII is definetly one of the best FF's, but VI is better imo.