I agree with Bloodfiredeath for the exact same reason. Stained Class does get most of the credit.
Sin After Sin is my personal favorite Judas Priest album. It is a very diverse record with many classics, and side two in particular is an incredible rollercoaster of emotion. It's almost exhausting to listen to! Incredible.
It is a bit like picking favorite children though. Sad Wings of Destiny is undoubtedly the most important melodic metal record ever made. It's production is incredible for the era, and all the songs are such landmarks. Same with Stained Class with the number of quality songs. I was ecstatic to see "Exciter" make it into the set list on JP's last US tour. And the title track is simply one of the best metal tracks ever written. Judas Priest were an incredibly, incredibly essential band for the history of metal for songs like this.
I do enjoy Rocka Rolla too. I appreciate it's "doominess" in places, it's raw emotion in tracks like the aforementiond "Run of the Mill", and I contend the multi-part "Dying to Meet You" is one of their most mysterious and powerful early-era tracks. Of all five of those though, Hell Bent For Leather is my least favorite. Don't get me wrong, it's definitely good, but I think it suffers from the first of Judas Priest's "silly" songs. I could have done without "Evil Fantasies" for one, and they kinda revisited a rock and roll feel with many others. When the album does get down to business though with some other stompers. But it does fit well in the progression with what was to be British Steel next...it's just that they blended the "rock and roll" aspect better on British Steel.
Anyway, early Priest is among my very favorite metal ever. Great thread.