"My main issue is the economy," he said. "I'm voting for Uhuru (Kenyatta) because he is younger and has a better vision to move the country forward."
At 51, Kenyatta would be the youngest Kenyan president ever. Odinga is 68.
'Things an average citizen worries about'
Harrison Mario, 37, said his vote is based on issues and policies, and will go to Odinga.
"Basically, he has been fighting inequality." he said. "He has been campaigning for the less fortunate. His manifesto focuses on security, education and food -- things an average citizen worries about."
Both leaders are campaigning on almost the same policies, leaving the more than 14 million registered voters to choose based on criteria that include personality, ethnicity and links to political parties.
"I don't know that much about their differences, so I'm voting for the candidate of my favorite political party," said Susan Kamau, who lives in Nairobi. "In short, I'm voting on loyalty to my party, not issues."
In addition to the presidential race, the nation will also pick governors, senators and a slew of other local candidates under the new constitution.
Whoever wins, the race evokes memories of a political dynasty.
Kenyatta's father was the nation's founding president, while Odinga's father was his vice president in the 1960s.
Both started out as allies in the fight for independence from Britain, but they had a falling out that led Jomo Kenyatta, a member of the Kikuyu tribe, to force out Jaramogi Odinga, a Luo tribe member, as his vice president.
Their history has strained relations for decades between Kikuyus and Luos.