I never really got into Maiden back in the day for some reason, always loved Sabbath and Priest. I finally listened to all of the Maiden albums last year for the first time. I found Number of the Beast to be a little overrated(Hallowed Be They Name is my favorite song of theirs but the rest of that album not that great). Piece of Mind and Powerslave are amazing 80's metal albums, I'd lean towards Piece of Mind being my favorite. Also really liked Somewhere in Time and Seventh Son. After that not much of their work does anything for me. Brave New World is good, can't really get into any of their most recent stuff.
The more and more I listen to their prime albums though I always end up going back to Caught Somewhere in Time. I'd say that album gradually became my favorite, album just has a certain 80's charm and feel to it that I really like.
I was super impressed with Maiden, listen to it a lot now, I'd definitely say they were better than Priest and Sabbath.