NBA: Lakers - Didn't jump on the bandwagon in the 80's. I was a Minneapolis Lakers fan in the 50's when I was a kid.
Major League Baseball: Yankees. I was a NY Giant fan and then a SF Giant fan until they traded Willie Mays, my favorite player. Became a Yankee fan in the AL in 1969 after Mickey Mantle retired - couldn't stand Mantle - and overall after the Giants traded Willie.
NFL: Giants.
Don't follow college basketball or football. College basketball has become a one year thing for most players who have talent, so there's little or no continuity there, except for the coaches (and not much continuity there either, these days). I enjoy watching basketball for the players, not the coaches. Most basketball coaches - and football coaches, for that matter - are obnoxious egomaniacs.
As I get older, I find that I have less investment in the teams I root for. I still root and follow my teams, but I don't have the ups and downs that I used have to after wins and losses. At my age, I've finally learned that it is, indeed, "only a game", and a game that I'm not playing, and that there are more important things in my life.