MAIDEN
I love Priest, but I get bored of them fairly quickly. Not the case with Maiden. Plus, I'll eventually check out anything new Priest does, but I will immediately blind buy any new Maiden. Their last 4 albums have been awesome.
For me, Priest's truly untouchable run was Sad Wings through Stained Class: 3 albums. I like most of their other stuff (particularly Defenders and Painkiller), but it's more hit and miss to me.
Maiden was untouchable from Number through Seventh Son: 5 albums. And I love everything else (besides the two with Blaze).