Honestly, Pet Shop Boys Discography is pretty perfect. Though Substance is up there too. For as much as I enjoy Staring at the Sea, I usually put on Cure LPs because start to finish I want to enjoy the mood of each particular LP. New Order's LP masterpiece (to me) is Technique. Substance captures great songs, but it also has a couple re-recorded versions. "Temptation" is great, I prefer the original version of "Confusion". I also prefer the LP version of "Bizarre Love Triangle".
So for me that's why "Discography" wins out. Start to finish, the selection and version of each song is perfect and the pacing of it all works beautifully for me. As much as I love "Behaviour" and "Actually", "Discography" is the first Pet Shop Boys LP I'll ever reach for. That's what a truly great greatest hits will do.
(Though the Jam's "Snap!" is up there too.)