Factbox: Argentina's presidential candidates and their policies

BUENOS AIRES (Reuters) - Argentines vote in a presidential election on Sunday billed as a choice between continuing free-spending leftist populism or a swing toward free markets to fix the South American country's ailing economy. [L1N13G0G8] The front-runner is opposition challenger Mauricio Macri, a two-term mayor of capital city Buenos Aires and founder of the "Let's Change" alliance, who promises pro-business reforms and an end to the confrontational leadership style of outgoing President Cristina Fernandez. He faces candidate Daniel Scioli, a moderate Peronist from the ruling Front for Victory Party who talks of the state maintaining a strong role in Latin America's No. 3 economy while promising gradual changes to improve the investment climate. Fernandez is barred by law from seeking a third straight term. Below are key facts about each of Sunday's candidates: DANIEL SCIOLI * A 58-year-old former power-boat champion who lost an arm in a crash in 1989, Scioli is the two-time governor of Buenos Aires, Argentina's most populous province. He is married to an ex model. * A former vice-president to Nestor Kirchner, Fernandez's late husband and predecessor, Scioli had been favored to win the election in the first round. But Macri's surprisingly strong showing dealt him a hammer blow from which he has struggled to recover, trailing Macri in the opinion polls. * Scioli has portrayed the run-off as a choice between a strong state as the guarantor of prosperity or a weak state that favors free markets and austerity. He depicts Macri as a right-winger who puts corporate interests before workers' rights. * He rejects the idea of an abrupt currency devaluation and defends the central bank's management of the official exchange rate. He vows to keep generous energy and transport subsidies. * Nonetheless, Scioli is viewed as more investor-friendly than Fernandez. He talks of gradual monetary reform and denies the country faces a crunch on foreign reserves. * In public, Scioli says negotiating a deal with U.S. "holdout" creditors suing over unpaid debt is not a priority. But in private his close advisors acknowledge Argentina needs access to financial markets and say Scioli would tap global credit markets once an agreement is reached. * In a flurry of last-minute policy pledges, Scioli has promised to increase pensions, send in the army to fight narco-gangs and restore credibility to the government's economic statistics agency. MAURICIO MACRI * Macri, 56, the son of an Italian-born construction magnate, became a household name in the 1990s as president of the fabled Boca Juniors soccer club. He cites his kidnapping in 1991 - his father reportedly paid a multi-million dollar ransom - as a trigger for a career in public service. * Macri founded and leads the center-right Republican Proposal party (PRO). After eight years as mayor of the capital, he is popular for cutting traffic, improving waste collection and sprucing up parks. * Macri has campaigned on a platform of change. He promises to begin dismantling capital controls on his first day in office to win investor confidence and bring hard currency into the dollar-starved economy. He will eliminate export taxes on corn and wheat and gradually reduce duties on soy shipments. * Other campaign pledges include restoring the independence of the central bank and judiciary, tackling corruption and nepotism in public offices and revamping the discredited national statistics agency. * Macri has won increasing support in low-income urban neighborhoods, traditional bastions of Peronist support but where some voters have become frustrated with decaying infrastructure and rising crime. * He has criticized Fernandez's failure to settle with Argentina's creditors in the United States. A deal with the holdouts would be a priority, his advisors say, although he would haggle hard. (Reporting by Buenos Aires newsroom; Editing by Mary Milliken)