Best song for me is still the unofficial epic The Mind's Eye - Portals - Shapeshifter. Love the melodies, the lyrics, and the instrumental is really impressive.
But for an "official" song, Visions is the best for me. The narrative is great, the music fit the narrative, and the feel is epic. And it also has Ray's best drumming performance.
Celestial Elixir is good, but what pulls it down for me is the lack of a climax. I think a long song always needs a climax so that there would be a payoff for listening to a very long song. Crystallized feels like a manufactured epic. The start is great, and then it descended into redundant and repetitive instrumentals that do not add enough variety to justify its length.