While I agree that Maiden is a very difficult band to cover successfully, there are a couple of covers that are actually superior to the originals in my opinion. First ist the Iced Earth cover of Transylvania. I haven't listened to the band since the storming of the capitol and don't think I'll ever listen to them again, but credit where credit's due I guess.
The other one's an Ides Of March/Purgatory cover by Steel Prophet.
I've listened to this version so much more that whenever I listen to Killers in its entirety I'm caught off guard when friggin' Wrathchild starts after Ides Of Mach

The additional guitar harmonies are all kinds of awesome as well.
About Cradle: I usually love their approach to covers (I adore their version of Devil Woman), but HBTN is a bit lacking I feel. I prefer their cover to the original studio version, but the Maiden live versions are superior of course.