Lusaka - Zambians flocked to the polls on Tuesday to choose the next leader of one of Africa's most promising frontier markets, in what shaped up as a tight race between a populist lawyer and a wealthy economist.Edgar Lungu, leader of the ruling Patriotic Front (PF), is seen having a slight edge over main rival Hakainde Hichilema, a businessman whose United Party for National Development has wooed the middle-class and investors.With no reliable opinion polls in the southern African state, few experts are keen to call a winner in the contest to succeed Michael Sata, who died in office in October aged 77.Lungu's campaign has focused on tapping into the grassroots support base of Sata, a populist leader from the majority Bemba tribe who won over the working class by funding infrastructure projects in poor, rural areas.Snaking queues"Michael Sata is still in the PF. We shall honour him to the letter," Lungu told supporters at his final rally in Lusaka.Hichilema, one of Zambia's wealthiest businessmen known locally as "HH", says he will draw on his experience in the private sector to attract foreign investment and diversify an economy, where copper accounts for 70% of export earningsHe has also promised free education for all, in a move aimed at gaining support among poorer Zambian voters."When your car has a problem you go to a mechanic. You need an economist like myself to fix the economy," Hichilema told his supporters at a rally on Monday, clad in Zambia's orange national soccer shirt.Voters braved the rain in many parts of the landlocked country to join snaking queues outside polling booths."I'm behind Edgar Lungu. He's a humble man. He's one of us," street trader Elvis Nyambe told Reuters as he waited to vote in Lusaka's Chawama township.PovertyJoyce Mainza, a 36-year-old mother of four, said she voted for Hichilema because he had laid out clear policy plans."We need someone who will get us out of poverty."With another election due late next year when Sata's term would have ended, whoever wins will have little time to turn around a stuttering economy.Zambia has averaged 6-7% growth as the mining sector boomed but growth slowed to 5.5 percent last year, the International Monetary Fund says, and could ease further with the price of copper at a 6-year low this month.A row between international mining companies and the government over royalty increases and $800m in unpaid taxes also threatens to deter investment.