The debut has the better songs, but weaker performances. We’re missing Adrian, but the album misses a lot even compared to bootlegs and live recordings from the time. I even like the Soundhouse Tapes versions of the songs a bit better. It’s raw and early Maiden is raw, but the production misses some of that early Maiden intensity. Maiden Japan and Live at the Rainbow
Killers is more polished, much better performed, Di’Anno sounds better, and there’s a really nice mix of live energy and studio magic. It’s what defined Maiden in the first half of the 80s. Because of that, I tend to listen to Killers more. It also has a lot of material that hasn’t been played live much. I have countless live versions of songs from the debut that are just better than what we got on the studio album.
As far as the material goes, it’s obvious that the best stuff made it on to the first album, but Killers has a lot of great overlooked material. I love Adrian’s guitar playing, the chemistry between the two guitarists, the more polished rhythm section, and Di’Anno has a lot more grit that I love. The album has a lot of cool tempo switches, classic Metal riffs, and just better captures the attitude of early Maiden. There are also hints of Number of the Beast and where the band was headed.
Taken against the rest of the discography, I would probably take both albums over everything from the 90s, although the debut, X Factor, and No Prayer are very close. I would very slightly take Killers over Dance of Death as well.