Short answers, pulled from the story.
The 1998 NBA Finals between the Chicago Bulls and the Utah Jazz was the highest rated and most watched NBA Finals series, averaging an 18.7 rating, a 33 share, and 29.04 million viewers on NBC.
CBS broadcast the NBA Finals through 1990, NBC held the broadcast from 1991 through 2002, and ABC has broadcast the series from 2003 onward.
The most watched single NBA Finals game was Game 6 of the 1998 Finals between the Chicago Bulls and the Utah Jazz, which drew 35.89 million viewers on NBC.
The 2020 NBA Finals hit a historic ratings low, averaging 7.5 million viewers over six games, a 51 percent decline from the year before. Some observers blamed the players' political activism, while others pointed to the COVID-19 pandemic pushing the Finals out of their usual season; the NHL and MLB playoffs saw comparable declines that year.
The 2019 NBA Finals, played between the Golden State Warriors and the Toronto Raptors, saw a drop in American viewership even though combined North American viewership held up. Canadian viewership does not count toward US Nielsen ratings, so the Raptors' run pushed Canadian audiences to record levels while only one US market appeared in the American numbers.
The highest rated single NBA Finals game was Game 6 of the 1998 Finals between the Chicago Bulls and the Utah Jazz, which posted a 22.3 rating and a 38 share on NBC.