Well it sure isn't the Americans.
And, to counter any "Ah but if we had our best players.." nonsense, just remember, that patriotism, and mental dedication ON THE COURT wins matches. Countless times in sport, the psychological strength of a team means a lesser talented team get's over the favorite.
American basketball/baseballers patriotism, national pride and mental dedication are so impressive that many didn't even show up for the games.
So, yes, those players are factored into the assertion that Cuba are the best baseball nation in the world right now, and that Italy or Argentina are the best basketball nation in the world right now.
Ahhhhhh don't ya love it??
Kind of like when the English first lost at cricket. Or football.