I agree that they should play Children Of Decadence. This song is really a masterpiece, 6 minutes of epicness! But from this list I chose Taste of my Scythe, I believe it's a very underestimated song. Tough choice though!
Yes, Children of Decadence is one of the songs they've been "playing" halfly, only playing the section before solos start. Other songs like this they've messed with include Towards Dead End, Bodom After Midnight, Mask of Sanity... they've turned them to combos / medleys with other songs... But Children of Decadence actually has epic atmosphere on the solo sections and it builds up to a climax. The band thinks it's too much unnecessary work to practice all the solos that nobody even recognizes, afraid that the intensity of the crowd dies during these sections.
Listen to the solo section: 3:30 - 4:35, it's fucking epic, and goes straight to the 2nd part of the chorus with epic, additional keyboard support at 4:35.
How does Alexi judge a live song working or not? He thinks a song "isn't recognized" by the crowd if there's no intensity in wrist banging or eye contact. I've come to the conclusion it's just the front row of teenagers who go crazy over their favourite tracks, but a more grown up fan can be just as thrilled and appear calm when a weird song like Taste of My Scythe or Knuckleduster is played. There's plenty of standard songs on the set like HCDR that really need not be played.