I tend to divide the best of Priest's career into 5 phases.
1. Early hard rock period - "Roca Rolla","Sad Wings of Destiny"
2. Early heavy metal period -"Stained Class", "Hell Bent for Leather"
3. Early Sell out attempts -"Point of Entry", "British Steel"
4. Stadium Rock period -"Screaming for Vengeance", "Defenders of the Faith"
5. Period of Decline -"Turbo" and onward.
The reason why I break up the albums like this is because Priest really is a different band in all these eras. Trying to rank albums is hard because they are of different styles in different periods. That said, I think "Sad Wings" is amazing. Les Binks, who will turn out to be a weak link when Priest gets heavier is in his element here. Halford's singing here also has not yet turned to screaming, and his voice can be admired for its range and his singing ability. "Stained Class" is the next album of mention. Here Halford's voice is turned into a metal voice by some clever effects and harder singing. "Stained Class" is just a great album, and is one of the heaviest albums I have ever heard period. Moving along, I think that "British Steel" is another album of mention. Here, Dave Holland replaces Les Binks on drums, and Oh what a difference it makes. Welcome the machine on drums -his playing is so loud and mechanical, almost clinical. "Point of entry" is one of their worst albums -so clear of an early attempt to sell out. Finally, "Screaming for Vengeance" and "Defenders of the Faith" are just outstanding. "Screaming" is more raw, and a little better in my opinion, but "Defenders" has a stadium sized bigness of sound that you will realize that this amazing band is at the peak of their career.