I think the low votes for Epica can be explained by the fact that they were the only band that didn't bring anything special. The setlist was predictable, no special guests, nothing unique about the performance. Even Symphony X played a rare song, and Russell Allen brought more energy (and banter) than I've ever seen at their tour shows. A run-of-the-mill Epica show, while naturally awesome, can't compete with the shows you could only see at ProgPower. (For the record, I loved their show; I just can't put it at the very top).
Serenity was my favorite. I was most excited for them going in, but they exceeded all expectations. Best mix/sound, incredible singing from both Georg and Clémentine, flawless vocal harmonies, and they had humor and great rapport with the crowd. The bands which are approachable, gracious, and genuinely happy to be there always seem to have the best performances (Circus Maximus is my early favorite for 2013).