The absolute leading 2:
1. Iron Maiden
2. Judas Priest
Candidates for the third place:
3. Midnight Oil / Bad Religion / Black Sabbath / Bruce Dickinson
This is really difficult because I love quite a lot of bands which have some amazing albums but also less interesting albums. Maiden and Priest had a few weaker ones, but the strong ones make up for it, so they easily stand above the other bands. I also love Rush and Helloween but relatively seen, I think The Oils, BR, Bruce and Sabbath had more consistent discographies. Rush and Helloween both had at least 5 lesser albums... and I am tempted to mention many more bands (e.g. 90s Iced Earth is excellent in my book)!