The two men represent starkly different futures for Latin America’s third-largest economy, creaking under triple-digit inflation after decades of debt, financial mismanagement and currency volatility, France 24 reported.
Polls show the candidates in a dead heat, with Milei holding such a slight advantage that no one wants to predict an outcome.
Polling opens at 8am local time (1100GMT) and closes at 6pm (2100GMT), with results expected a few hours later.
Massa, 51, is a charismatic and seasoned politician seeking to convince Argentines to trust him despite his performance as economy minister which has seen annual inflation hit 143 percent and record poverty levels.
His rival Milei is an anti-establishment outsider, who has vowed to halt Argentina’s unbridled spending, ditch the peso for the US dollar, and “dynamite” the central bank.
Most are so disgusted with their options that “they’re going to have to choose the lesser of two evils.”