Finally caught up. Somehow I missed seeing the start of this thread in May, and then just needed to carve out a couple hours to read and catch up. So, bit of a long post here...
The Di'Anno albums - I didn't get them until much later into my Maiden voyage. They didn't start out too well for me, but have aged very nicely. Some real gems in there. Like JJ said, they are sufficiently metal enough to listen past the punk style.
NOTB
My favorite Maiden album - virtually flawless (especially when you swap Gangland with Total Eclipse). Hallowed is my #1 Maiden song of all-time. I don't have enough superlatives for this album. Run To The Hills was the first Maiden song I ever heard - probably at 15 yrs old (and through the video - Tim... thanks for posting that. It was still getting regular rotation up here on Much Music into the late 80s. Gave me chills to watch it). For me, it's one of those songs that invokes the feelings that I had the very first time I heard it - like a shadow, that feeling is always with me when I hear it. Jaw dropping. Everything about it was like nothing I'd ever heard before - the vocals, the drum fills, the solo, the galloping bass.
Fun story... in the late 80s, for a few years in a row, me and a few buddies would make a weekend road-trip to Boston after exams in May. We'd drive all night on a Friday, go to a bunch of CD shops and spend a shit-ton of money on CDs, get all lathered up at Faneuil Hall, more shopping on Sunday and drive home Sunday evening. One time, around 5am Saturday morning, RTTH comes on, and our driver at the time is air-drumming his way through every fill - to the point that we're making a turn on a winding and hilly road, and he almost takes us over the edge - BECAUSE HE HAS TO FINISH THE DRUM FILL!!! Buddy in the passenger seat was luckily not napping, and had to yank the wheel to get us back on the road.
This is definitely the flagship album in their discography. No doubt about it. Some may argue that it isn't their "best", but it is their flagship.
PoM
As has already been implied, Nicko made an impact in the first 15 seconds of the album. His work on the Where Eagles Dare is unreal, and a noticeable step up from Clive. This was actually my first Maiden album, and for me there isn't a weak track on the album. I love them all. Song-for-song, it's their most consistent album imo.