In terms of actual basketball, I think it's either Boston/Denver or Boston/Minny. Both matchups are really close matchups with similar level teams that have only minor differences in their top levels. There's also plenty of star power and contrasting gameplans/philosophies to make it really interesting. Also, all of these teams have legitimate arguments to be the next dynasty given their rosters and expectations, which adds intrigue.
In terms of viewership, it's clearly New York versus Dallas just in terms of market sizes, I think.