Well, a good guitar solo will usually have me smiling from ear to ear while playing air guitar (or, if I sit with my guitar, play along when I can and if I can't I just play the rhythm part).
I'll name solos I love from each album.
Iron Maiden: Phantom of the Opera has great solos, I also like Dave's in Prowler.
Killers: Who can
not like the solos in the title song?
TNOTB: Some great here as well. Children of the Damned has a great one from H, I also like the guitar in The Prisoner and of course it would be a crime not to mention Hallowed Be Thy Name. Great stuff from both of them.
Piece of Mind: Hell, I like nearly all the guitar solos on this album, so to make it simple I'll just go with the duel in The Trooper.
Powerslave: The first part of the Powerslave solo (not to mention the Live after Death version of it) is breathtaking, and Rime of the Ancient Mariner contains the finest three minutes in heavy metal. These three minutes include solos from Adrian and Dave
Somewhere in Time: Adrian's solos on CSIT and SIASL are the greatest moments on the record and both guitarists do great stuff on Alexander.
Seventh Son of a Seventh Son: The title track and The Clairvoyant
No Prayer for the Dying: Dave and Janick both deliver on Mother Russia. Janick's solo in Holy Smoke deserves mention just because it's so different.
Fear of the Dark: The best is in the title track, no doubt. And my next project is to learn Janick's solo in this song.
The X Factor: Good stuff in Sign of the Cross, and both in The Edge of Darkness.
Virtual XI: The solos in The Clansman stand out for me.
Brave New World: Lots of good solos on this album. H in The Wicker Man, Janick in Blood Brothers are the first that spring to my mind. Dave's solo in Blood Brothers is also great.
Dance of Death: I really like Dave's work in Rainmaker, the three-man relay in No More Lies and the solos in Dance of Death. And of course Paschendale.
A Matter of Life and Death: H in These colours don't run, Dave in The Longest Day and Janick's in The Legacy are all very good. And both (yes, both) in Lord of Light.
How to pick one of all these as a favourite? Hard, very hard. But I'm gonna stick with Rime of the Ancient Mariner. When Adrian's first note hits my ear, I start smiling and I keep smiling until the singing starts again. (The reason to stop smiling is of course that I always sing along with Bruce
)