I, sadly, do not own Rocka Rolla or (perhaps less sadly) either of the Ripper albums, so I have to make my decision without having heard much from either of those. I also haven't been able to find my copy of Stained Class for like two and a half years, so... Luckily I have the Metalogy so it's not all bad. ANYWAY...
I picked Sad Wings of Destiny and Hellbent For Leather. I used to really love 80's (and onward) Priest material, but I simply don't enjoy it these days nearly as much as I used to. 70's Priest is far superior (this is actually a scientific fact). I just feel that they were a lot more creative and different back then.
By the way, anyone know when the new album is supposed to come out? I really don't know what to expect.