For NFL- I root for 2 teams because some AFC and NFC teams rarely have matches against each other. The 2 teams being SF 49ers and PIT Steelers. The dream of course is a super bowl between the 2. The 2 teams are actually 11-10 in favor of 49ers, so 21 games in over 67 years. About 1 game per 3 years, so I think being a fan of 2 teams is quite reasonable otherwise there will be many games that I just don't care about.
MLB- I like the Cubs.