Man this is tough.
Though I think I'll have to go with "Adhesive." I became an STP fan through Velvet Revolver and really fell in love with Tiny Music... last summer. And I just remember driving around at night and when that song came on, it was just so serene. I absolutely LOVE when it picks up and starts chugging along, with Eric moving ahead and behind the beat, not to mention Rob's bass and Dean's psychedelic tone. Just a great composition.
And in response to the above post, I find the ending of "Seven Caged Tigers" to be one of the best album-closers I've ever heard. It's eerie but it works so well. I love how it carries you away into silence.