Although 14 candidates are contesting the election, these two men are the frontrunners with most eyes on them.
The elections in Africa's biggest oil producer come at a politically sensitive time, with the rise of Islamist group Boko Haram in the north-east meaning security is at the centre of the campaigns for votes.
Nigerians discuss their experience of the election campaign with the BBC and say whom they plan to support.
I am voting APC this time, though I voted People's Democractic Party (PDP) in the last presidential election.  This is because PDP has been in power for over 15 years and we haven't really progressed.
Our leaders need to understand Nigerians decide who leads them. I have no sympathy for any political party. I simply want the best for my country.  We have tried PDP and they have failed.
Now is time for change.
Nigeria has abundant resources (human and natural) to be  amongst the world's greatest nations. We need a compassionate, visionary, strong-willed leader to lead us to our rightful place.
Kill corruption and Nigeria will not only live but prosper. Buhari is certainly not the "Messiah" but he surely can be the forerunner. He can help lay the right foundations for a new corrupt-free Nigeria.
I'm supporting President Goodluck Ebel Jonathan because he is a true democrat.
He is building institutions in Nigeria and giving them the free hand to tell between good and evil.
He is a true Nigerian - patriotic and loyal.
No past leader compares to GEJ in democracy,  performance and transformation.
I am not voting because of the candidates. They don't meet my standards. Corruption is the biggest problem in the country.
Goodluck Jonathan is weak because there is a lot of corruption in the land and he hasn't confronted it.  Muhammadu Buhari could not deal with it in my opinion - he doesn't have enough brains.
I would prefer a balance of 50% ability to fight corruption and 50% ability to handle the economy. The other guys aren't popular, the more well-known candidates over-shadow them.
People are eager and are waiting to see what happens.
This election is divided. Now people don't see themselves as Nigerian but rather by their ethnic group.
Nigeria's presidential elections, taking place this Saturday, will see a showdown between incumbent President Goodluck Jonathan and former military ruler Muhammadu Buhari, of the opposition All Progressives Congress (APC) party.