Opinion polls give Mario Abdo Benitez of the ruling conservative Colorado party a clear advantage over lawyer Efrain Alegre from the centrist GANAR coalition.
Here is a look at the two candidates:
Benitez: linked to a dictator
Mario Abdo Benitez's family has long been linked with late dictator Alfredo Stroessner, but it doesn't seem to have done his campaign any harm.
A twice-married 46-year-old former senator who studied marketing in the United States, "Marito" as he is popularly known, is favorite to succeed outgoing president Horacio Cartes. Opinion polls give him a lead of some 20 percentage points.
His father was Stroessner's private secretary, and they also had a family connection.
"What they tell me is that Stroessner often stayed at my grandmother's house when he came to Asuncion to study at the military college, because there was a distant relationship between my grandmother and the mother of General Stroessner," he said.
But past connections with the dictator accused by human rights groups of up to 3,000 killings and disappearances during his iron-fisted 1954-1989 rule have been left aside in the electoral campaign.
"Those who are less than 40-years-old no longer remember the dictatorship, which is why it is not part of the discussion in this campaign," according to political analyst Francisco Capli.
"I am proud that the victims who suffered mistreatment and torture at that time are working with me today," Abdo told AFP in an interview. "This is another era. If I had been rejected, they would not be with me."
Abdo is a product of Paraguay's high society but he claims to have forged his own political identity since entering politics in 1992.
"I regret the dark part of our history, but like many Paraguayans I think it should not be an excuse to maintain division among compatriots," he said. "I was 17 when Stroessner fell."
His father was jailed for corruption in the wake of Stroessner's fall.
"I want to show that my commitment is to the future of Paraguay."
Alegre the outsider
For his 55-year-old rival, former public works minister and parliament president Efrain Alegre, "Marito represents the past."
A practicing Catholic opposed to abortion and gay marriage, his conservative views contrast with some of the parties in his centrist GANAR Alliance.
Alegre has advocated slashing electricity bills, citing cheap power available from the country's Itaipu dam -- the world's second biggest -- as well as free health care for the country's poor, which has led to rivals branding him a populist.
"Macroeconomics doesn't feed the people," he said, rejecting as official propaganda government statements playing up 4.5 percent growth in 2017, among the highest in Latin America.
Being an anti-Stroessner militant in his youth led him to study law.
"For me, studying law meant youthful rebellion and I thought it was an important instrument to use to fight against the dictatorship," he told AFP in an interview.
Alegre is contesting his second presidential election in five years, having lost out to tobacco magnate Cartes in 2013.
The eighth of 12 sons of a landowner from the southeast, Alegre says that decades of conservative Colorado governments have been synonymous with "instability, poverty, waste and corruption" in one of Latin America's poorest countries.
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