I feel Dante by the end of DMC3 has got the higher chance of winning by cheer experience. All the Bosses Nero has fought were pushovers excluding Dante who wasn't fighting to kill. Dante went through 3 fights with Vergil that basically pushed him to his limits each time as well as fighting Arkham which required Vergil's help to defeat. Nero has never experienced such fighting and has simply gotten by from brute strength while Dante needed to learn from defeat and the constant threat of Vegil killing him in each encounter.
"DMC4 is the best entry in the series"-AlexxShadenk777
According to an old interview, Nero was supposed to be on par with DMC3 Dante by the end of DMC4. So in a battle without plot-armor, I'd say its a tie. It should easily go either way if we ignore the plot armor Dante automatically gets as the series main protagonist.