Do you really need to ask me?
Halford/Dickinson - Bruce easily. Rob has a better range and great screams, but he doesn't know how to use them effectively. I refuse to believe that "Painkiller" is a good vocal song. Halford's screams are best in moderation. Bruce's range is only a tad smaller than Rob's, and his screams are not only better, but more controlled. Also, since blowing out his voice, he can actually sing better. Figure that one out.
Tipton & Downing/Murray, Smith, & Gers - Maiden easily here as well. Murray and Smith perfected what Tipton and Downing forged, and no one does it better than the Maiden duo. Add Gers (sloppy though he can be) into the mix and you've got a freakish triple-lead monster. Murray has the greatest guitar tone I've ever heard, and it compliments Smith's more traditional metal tone perfectly, and they are both complimented by Gers' rather uncontrollable sounding tone. Tipton and Downing both sound very alike, with no way to distinguish between the two very easily. Their riffs were not only less complicated than Maiden's, but they were also less compelling.
Hill/Harris - Not really a contest here. One of metal's greatest (Harris) against the most boring bass player in recent history.
Priest drummers/Burr & McBrain - Maiden wins again. Burr and McBrain are quite simply two of the most technically skilled drummers to grace metal. McBrain being the wack-job amalgam of Keith Moon and Neil Peart, Burr being ridiculously clever with his guitar following fills and blindingly fast rolls. The Priest stable of drummers are average at best. Sure, the tracks from Painkiller are great, but one album of decency cannot stand against the drum onslaught Maiden brings every time they play.
Overall - Iron Maiden quite easily. Better songs, better lyrics, better talent...