I have always loved Sister, I guess because as others have said the lyrics relate to me but I also love the music.
I don't really have a least favourite song, but the songs that took the longest to grow on me were Illusion and Unforgiven, I think these are much better live and i really only fully appreciated these songs untill after I had heard the live versions, these are now some of my favourites.
What if the sun refused to shine?
What if the clouds refused to rain?
What if the world refused it's turn?
What if the clocks would hesitate?
What if what is isn't true?
What are you going to do?
What if what isn't you?
Appels and Oranjes - Smashing Pumpkins