Wasted Years without a doubt at the top. Also like pretty much all of Somewhere in Time and Seventh Son of a Seventh Son. After that it's here and there like Number of the Beast, Holy Smoke, Run to the Hills, etc.
I will say that you haven't heard Maiden in all their glory unless you've seen them play live. Seriously, if you haven't, you need to find a way. They are simply unbelievable live. Lots more solos, crazy stunts like rubbing the guitar strings on the amp stacks, every concert series has its own props like giant Eddies. I was 100% sober and it blew my mind. Only band I ever saw that was close to as good a show was Judas Priest. Metallica, Megadeth, Slayer, Anthrax all paled in comparison.