I voted Dave but it was a very tough call.
Adrian- He is probably the greatest guitarist of all time when it comes to structuring a solo. It is very easy to split his solos into sections.just listen to the tropper, caught somewhere in time or number of the beast. The guy will perform a lick for 3/4 of a bar, have a small transition phase and move n the next. His solos are works of art. He is also the best songwriter of the 3 and has written many of the bands best songs including Paschendale, Starblind, Brighter than a thousadsuns, Wasted years and The Prisoner.
Janick- Janick has proved that he can write and play exellent solos. Listen to Sign of the cross Wasting love, The Legacy, Blood Brothers, Como estais Amigos and 2am for hs best work. The problem is he is nowhere near as perfect as H and Dave an can butcher solos live. His stage presence (sp?) is phenomenal and he really tries his best and gives each show his all. Janick is also an excellent songwriter. Dream of mirrors, Danceof death, Ghost of the navigator, The legacy,The talisman, como estais amingo. enough said.
Dave- He has been in maiden from the beginning. As far as im concened Dave murrays sound is iron maiden. He played a major role in creating the legendary, influencial sound that is iron maiden. Dave has proved that he can solo. Whether it be lightning fast (brave new world) or slow ( powerslave ) His solos are always smooth and melodic and he has developed a legato technique that could possibly be the best in world. His songwriting skills are good ( TLBLAH, stillife, breeg etc ) but his first powerslave solo for me is greatest guitar solo ever.