It would be like basketball. I'd watch, but all my passion would be gone. I really couldn't pick a team. I've tried in basketball and hockey, but my passion around sports really revolves around the team I grew up with, so I can't generate fake passion. I will never feel closely connected to teams outside of KC, because that's the town I grew up in and established an identity with.
That said, if you forced me, it would be the Niners, because I grew up rooting for Montana and I could continue to hate the Raiders...