"The big risk of this election is that it will return us to an era of crisis," said Sahondra Rabenarivo, an analyst at the Malagasy Observatory on Public Life.
"It's very important that the results are credible and that the third-placed candidate accepts them," added Rabenarivo referring to the leading hopeful who will not advance to any second round.
Tensions are high between Ravalomanana and Rajoelina, who succeeded him with the backing of the army in the 2009 uprising.
Madagascar is one of the world's poorest countries, according to World Bank data, with almost four in five people living in grinding poverty.
Many voters see the delivery of basic resources like water, electricity and jobs as their priorities.
The trio of main contenders — armed with significant campaign resources — have criss-crossed the island of 25 million by helicopter promising voters a better future.
"It's a circus," added Rabenarivo, the analyst.
An EU-sponsored study found that Rajaonarimampianina spent $43 million on his 2013 campaign — $21.50 for each vote.
"The people are sick of the (leading) three candidates. Their time in power has been fruitless," said rural voter Mari Rajafinniana who told AFP he planned to vote for candidate number 11, Ny Rado Rafalimanana.
Although there were bloody protests in April that left two people dead, campaigning has so far gone smoothly.
The candidates have however been accused of vote buying. The head of Transparency International in Madagascar, Ketakandriana Rafitoson, is "disgusted" by what she says is the handing out of T-shirts, sewing machines and even floor tiles to buy votes.
The election will be seen as an important opportunity for rivals Ravalomanana and Rajoelina to settle their scores through the ballot box, according to commentators.
Both were banned from contesting the last elections in 2013.
Ravalomanana, who until 2014 lived in exile in South Africa after his removal from office, is still bitter after his ouster by Rajoelina in the coup that left the island internationally isolated and bitterly divided.
Rajoelina, a former mayor, party planner and successful entrepreneur is banking on his youth and communication skills to rally support.
Around 20 lower-profile candidates have alleged irregularities in the electoral roll and have unsuccessfully called for the poll to be delayed.