The outcome of the election will determine the speed and depth of reforms needed to kick-start growth, restore the central bank's near-empty liquid reserves, narrow a yawning fiscal deficit and tame high inflation.
Scioli, a moderate within the broad Peronist movement that dominates Argentine politics, plans to unravel some of Fernandez's policies but pledges only gradual change and says he will stick with her popular welfare programs.
"We are what's known, and people are not in the mood for experiments," Scioli said on Thursday, the last day of campaigning.
His rivals, center-right Mauricio Macri and centrist Sergio Massa both promise to move faster to open up Latin America's No.3 economy.
To win outright on Sunday, Scioli needs 45 percent of votes, or 40 percent with a 10 percentage point lead over his closest challenger. Polls show him hovering near the 40 percent threshold and Macri approaching 30 percent.
The election marks the end of 12 years of "Kirchnerismo" covering the presidencies of Fernandez and her late husband and predecessor, Nestor Kirchner. They are credited by supporters with reviving growth, protecting Argentine industry and helping the poor after a massive economic crisis in 2001-02.