That's like obtaining the entire Lakland or Sadowsky inventory and trying to choose which one to gig tonight...you'd have to switch basses for each song and you'd still be overwhelmed!
Watching them live even makes it harder to pick a song because they add such cool bridges and stuff...not to mention they really connect well.
They have so many strong songs...Schism, Aenema, Lateralus, The Patient...jeez the list goes on. I've been listening to them strongly for the past 3 years (since my Sophomore year of high school, now a college freshman. Known about them since they released Lateralus when I was around 7th grade) and i've yet to tire out from them.
I can honestly say there isn't a tool song I don't like, and that's going from Opiate to 10k Days, including Salival.
However, for the sake of the thread I will say Aenema. I'm not even gonna bother saying why I like it.