Voted with the herd on Nightwish. First pair was closer, didn't realize my vote would put one of the songs in the lead. There were things I didn't like about each. Odyssey was too long.* It dragged in places, and it seemed like they started with the idea they wanted to create a song that would fill an LP side, and they had about 15 minutes of good ideas, but the remaining 10 were filler. But those 15 minutes were very good. The style of Crimson King is VERY dated, 60s-hippie-psychedelic, which I don't love. But as a song, on its own merits, I thought it was better. Obviously, Odyssey rocks harder, but the melody in Crimson King is haunting and quite beautiful. So, I voted for King Crimson.
* I'm finding this to be a reaction I have to many of the songs in this game. Too many seem to be long for length's sake. There are some 3-hour movies that are gripping throughout (e.g., Pulp Fiction, Godfather 1 & 2, LotR trilogy), and many more that are boring and drag (e.g., The Green Mile). If I think one of these "epics" strays into Green Mile territory, there are far less likely from getting my vote. Odyssey is not it THAT league, but this is a rough guideline in my mind.