São Paulo FC, by heritage. I also happen to live near the club and my parents are members.
My earliest vivid (and painful) memory is the 1990 Brazilian Championship when we reached the final and lost to our rivals Corinthians 1-0.
My best memory is a tough call between winning the Toyota Cup for the first time against Barcelona (coming back from 0-1 to win 2-1), and the Libertadores title in 2005 when we thrashed Atletico Paranaense in the final 4-0 and I happened to be at the match.
So you had it in the family, there wasn't too much choice, hehe.
Yes, I remember the Toyota Cup when they beat Milan. Rai scored with the chest and then Muller scored with his arse.