Go with "Painkiller" if you're between the ages of 15 and early 20's, all the real old stuff is great but it aint gonna get a young dude hooked on Priest.
"Hell Bent for Leather" (Killing Machine outside the U.S.) should be next Les Binks was giving a clinic in early metal drumming without even knowing it. Then "Stained Class"
I think Jugulator is a case for judgeing an album by it's cover... very fucking brutal, even if I do prefer Demolition for the Ripper-era stuff.
As for Priest albums to get?
British Steel, Sad Wings of Destiny, Painkiller, Angel of Retribution... and probs Halford's Live Insurrection to start with...