For me it i think is IBB. The gap-tooth evilgenius is known from every corner of the country.
Soyinka cannot be the most popular Nigerian. More than half of the population which are illiterates do not know him. Kanu or Okocha or even some Nollywood actors/actress are more popular than any other Nigerian. The other popular Nigerians would of course be IBB, Obasanjo and Ojukwu. Anybody who knows about the Biafra war must know the name Ojukwu, and from what we see on nairaland, Ojukwu is a very popular name (for good or bad, depending on where you belong). The muslim Nigerians (at least 50% of the population) do not know Adeboye, let alone him being popular amongst them.
I think you guys need to understand the difference between being popular and being famous.
Being popular means liked or admired by many
Being famous means known to or by many
Methinks the current most famous Nigerian is Obasanjo. Every Nigerian knows him, while the most popular Nigerian is Pastor Adeboye. Wonder why he's one of the most influential people in the world.