If, as many polls predict, Modi wins a fourth term as chief minister of the state, he is expected to project himself as the presumptive prime ministerial candidate for his right-wing Hindu nationalist Bharatiya Janata Party (BJP) in a general election due in 2014.
Gandhi's ruling Congress party has declared that he will be the face of its election campaign but has stopped short of saying he would become prime minister if the party was re-elected for a third term. Nevertheless, he is widely viewed as the party's top candidate for premier.
While analysts warn there is no certainty that either man will become their party's nominee for the top post, many in India are already talking about a potential Modi vs Gandhi clash in 2014 that would pit the charismatic but controversial chief minister against the heir to the country's first family.
Whoever becomes prime minister will take the helm of Asia's third-largest economy at a critical juncture in India's history as it tries to lift millions out of deep poverty and make the leap to become a global economic power.
Gujaratis are voting in a staggered election, with the second vote on Dec. 17. The results will be published on Dec. 20.
The margin of Modi's victory will help determine whether he wins his party's backing to lead the election-year charge. Analysts agree that Modi, 62, would be a formidable foe for the Congress party if he can triumph over both BJP infighting and fears within the party and its allies that he is too divisive a figure to take on the dynasty that has ruled India for most of the post- independence era.
Critics accuse Modi of not having done enough to stem riots that killed between 1,000 and 2,000 people, most of them Muslims, in Gujarat in 2002, an accusation he denies. His supporters point to the economic boom he has presided over in the western state since first coming to power in 2001.
"Chief minister Narendra Modi has a solid track record of over a decade to flaunt. Rahul has no experience of running a government. His biggest asset is his surname," a minister in Modi's cabinet told Reuters on condition of anonymity.
In the run-up to Thursday's poll, Modi has criss-crossed the state in an effort to improve the 117-seat total the BJP won in 2007 and dispel any notion that his popularity may be waning. His election team, who call themselves "Modi's Men", have even rigged up a 3-D projection of the stocky, bespectacled Modi to allow him to appear "live" on stage at simultaneous events.
Rahul Gandhi, 42, in contrast, stayed away from Gujarat until the last day of campaigning. Analysts said Congress is certain to lose the election and its leaders do not want Gandhi associated with defeat again, after his failure to lead the party to victory in Uttar Pradesh state this year. But Congress has been keen to show Indians that the reclusive Gandhi is more than just a name and is taking on more leadership responsibilities within the party, although his mother, Sonia Gandhi, still has the final say as Congress chief.
"Rahul is going to lead the party into the next general elections," a senior Congress party official said after Gandhi was named the head of its election committee. "Rahul has to take over (the party) but when and how is a call he will take."
Aarthi Ramachandran, author of "Decoding Rahul Gandhi", said the Congress party would do its best to avoid turning the 2014 election into a personality contest between Gandhi and Modi, if the two men emerged as their party's candidate for premier.
"Rahul Gandhi's personality does not lend itself to the putting up of a mesmerizing electoral show. He struggles with public speaking, and connecting with crowds and cadre," Ramachandran said.
"Modi is nothing if not a performer on stage, and has a track record of being one in office as well. Rahul struggles here too. In his eight years of political life, Rahul Gandhi has few deliverables under his belt.
At the level of a personality contest between Modi and Rahul, it would be a no contest."
The two men would likely offer Indians sharply contrasting visions of how to grow the economy, improve competitiveness in a more globalised economy and build a bigger middle class in a country of 1.2 billion.
Modi's claim to fame is as an effective economic manager whose pro-business policies have attracted billions of dollars of investment and swept away obstacles to foreign and domestic companies setting up shop in Gujarat.
"Modi has been good for the business community. We are hoping that he comes back to power," said Chandrakant Sanghavi, a prominent diamond businessman from the Gujarat city of Surat, a global diamond-polishing hub.
It is not clear, however, whether Modi could translate that success across a country where powerful regional parties increasingly hold sway and states are seeking to chart their own course by reaching out directly to foreign investors. Gandhi's vision for the economy is less well known but in his relatively few public utterances on economic issues he has backed expensive social welfare policies favoured by his mother.
Whatever their economic visions, both men will struggle to implement them as the 2014 elections are expected to produce an even more fragmented political landscape in which coalition politics will make bold reforms difficult.