I will go with the NBA but I think it's closer than people think.
Throughout the country, a lot of Whites and Hispanics f*ck with baseball more than basketball and they'll sign their kids up to play baseball over basketball on average.
Also, like football, baseball has an older target audience that's more likely to religiously follow the games and contribute to ratings whereas the NBA has a lot young bandwagon fans who only stan a few players with decent narratives(not even a team) and follow highlights without watching a single game.
Even Stephen Smith made that mistake a few years ago where he claimed that Baseball was basically Larry Holmes flabby and sick while the NBA was growing but people wounded up debunking that narrative by showing the ratings stats that showed that MLB and NBA games had similar ratings and there's still times where MLB draws more viewers than the NBA.
Now, I know some will chalk this down to race and politics but the highlights culture has turned a lot of young NBA fans who people like Stephen were betting on to make the NBA the top sport into basically hypebeasts who mostly dikkride who's trending or has a narrative surrounding them atm while barely even watching the games outside of highlights.
I still think the NBA is popular but the gap is pretty narrow overall.