With me it comes down to #3 vs #5.
Why not #8?
Well, #8 was another great candidate because it includes my favourite song Rime of the Ancient Mariner. Further we got Alexander the Great, Only the Good Die Young, Blood on the World's Hands & Paschendale. However I'm not that over the moon about Paschendale as most of you guys, and -more important-, this group contains:
Chains of Misery, Como Estais Amigos, FTGGOG (all three belong to my least favourite songs from their corresponding albums) and the pre-Powerslave albums tracks are not the best ones either.
So what's left? Here goes (in bold the songs which belong to my favourites):
3:
Remember Tomorrow, Murders in the Rue Morgue, The Prisoner, Flight of Icarus, Losfer Words (Big 'Orra), Sea of Madness, Can I Play With Madness, No Prayer for the Dying, Afraid to Shoot Strangers, Man on the Edge, Lightning Strikes Twice, Brave New World, No More Lies, Brighter than a Thousand Suns
5
Phantom of the Opera, Genghis Khan, The Number of the Beast, The Trooper, The Duellists, The Loneliness of the Long Distance Runner, Seventh Son of a Seventh Son, Fates Warning, Childhood's End, Look for the Truth, When Two Worlds Collide, The Mercenary, Dance of Death, The Longest Day
Category 3 has less weaker tracks. I only dislike No More Lies.
Category 5 has two weaker tracks, namely When Two Worlds Collide & The Longest Day.
Still, I decided to choose for #5, because it contains quite some more awesome tracks. So many strong ones, a great playlist! But it was hard. #3 and #8 were worthy opponents and who knows, this might change another day.