I don't know what the "best" song is; they are all very good: both catchy in tune and have thoughtful lyrics. My favorite Epica song right now would be The Phantom Agony. There's a lot of truth in the lyrics.
Hello jcdevil! I'll just go with the flow when saying cry for the moon it the best song of this album. Although sensorium also rocks. I also love The last crusade from Consign to Oblivion.
Have a nice day!