Purple.
It's just the feeling I get, but a little analysis: the momentum, you just really hear where the band is at. Full of creativity and better players (after all that touring). Like Scott said himself, dope made him confident at first (being the time Purple was being written). He isn't afraid to go into personal lyrics, and man the melodies are incredible! Where Core was still a little dour at times, if you will, Purple has enough of that "fun factor" too - Interstate, Big Empty sound like incredible summer classics, Lounge Fly is great and really the first really trippy song they make. Still Remains, sort of "trippy" too, but first and foremost - the friggin melody! Silvergun, Army Ants and Unglued are there to give the harder side and they fit in just like the rest.
I guess for me, this album defined stp. Not too soft, not too hard, just incredible pictures in my head when I listen to this record. Purple is like a perfect summer day and evening.