Bespectacled and mild-mannered, the Socialist Hollande - tipped to win the vote - has promised to be a consensus-builder and a "normal president" in contrast to the hyperactive right-wing incumbent Sarkozy.
Sarkozy was elected in 2007 with 53 percent of the vote on a wave of optimism over his dynamic style. He was briefly the most popular president since General Charles de Gaulle, but his star rapidly faded.
Five years on, after promises of wealth and job creation proved a mirage, Sarkozy's aggression grates for many voters, and he is seeking re-election with the worst opinion poll approval ratings in modern French history.
His initial "bling-bling" style, with dinners at glitzy eateries, a luxury yacht holiday and his marriage to supermodel Carla Bruni, hardly helped.
Nicolas Sarkozy de Nagy-Bosca retains the boundless ambition that drove the son of a Hungarian immigrant, with no ties to the Paris elite or the provincial bourgeoisie that dominate French politics, to the presidency.
His supporters point to the reforms that he managed to push past a dubious parliament and public - an unpopular increase in the retirement age from 60 to 62 and a measure to ensure the independence of universities.
He has had an impact on the international stage, helping negotiate an end to Russia's drive into Georgia and leading the NATO intervention that helped Libyan rebels topple Moamer Kadhafi last year.
French banks - and the euro - remain exposed to the sovereign debt crisis in the eurozone, but neither collapsed on his watch, and while the French economy is suffering, it is in better shape than Italy's or Spain's.
Hollande, a protege of modernising former European Commission chairman Jacques Delors, is of the generation groomed under the last, and only previous, Socialist president, Francois Mitterrand, who left office in 1995.
A local lawmaker and party activist, Hollande led the Socialists for 11 years but has never held a top government post.
He was elected as candidate in October after a US-style primary that saw him hailed as a moderate and a unifier, but also derided as "wishy-washy".
A former partner of Segolene Royal, whom Sarkozy defeated in the 2007 presidential vote, Hollande is now in a relationship with political journalist Valerie Trierweiler.
She reportedly encouraged him to lose 10 kilogrammes (22 pounds) of unpresidential body fat and adopt thinner-framed glasses for the campaign.
He is running on a classic Socialist platform, with promises of boosting taxes on the rich, increasing social spending and creating tens of thousands of state jobs.
He has worried some with declarations that the "world of finance" is his "enemy" and vows to re-negotiate a hard-fought eurozone fiscal pact, but experts say Hollande would likely be a pragmatic leader.
The Socialist remains the frontrunner in the race, with polls showing him with a comfortable lead over his right-wing rival for the May 6 second round of the presidential vote.