Which of the following explorers would you consider most significant to the age of Exploration and why?
Cabral: Reached Brazil and claimed it for Portugal
Amerigo Vespucci: Traveled the coast of South America; Claimed the land was not Asia but a "New" World
Ferdinand Magellan: Credited with sailing around the world
Hernando Cortes: Conquered the Aztec Empire in Mexico
Francisco Pizarro: Conquered the Incan Empire in Peru
Ponce De Leon: Landed on the coast of Florida and claimed it for Spain
Coronado: Searched Arizona, New Mexico, Texas, Oklahoma, and Kansas searching for gold
It is difficult to assess "one" level of importance in assigning primacy to different explorers. I suppose that if one lived in one of these areas and whose own narrative was impacted by these examples of colonization and eventual imperialism, I would think that specific instances might stick out more in one's mind. For example, if one lived in Mexico and sought to understand their history as one of struggle and oppression, then Cortes' exploration and subjugation of indigenous people and leaders would have more relevance than some of the other explorations. This helps to underscore a basic thread in all of these ventures in that each of them set out to control and dominate what was not the explorers' to overtake. The use of exploration and venture quickly morphed into control, domination, and subjugation. Each of these examples of the greatness of exploration came with an incredibly high price tag for indigenous people.
I'd have to agree that Magellan remains the most important out of the group you list. His voyage proved conclusively what Gautier de Metz wrote in L'Image du Monde in the 14th century, that a man could make a journey around the world "as a fly makes the tour of an apple." I'd have to point out, though, that Columbus, as vilified as we was late in life, was certainly the most important of early Spanish-Portuguese explorers for having been able to mount the first major voyage across the Atlantic and into the unknown. Despite earlier landings in the New World over a period of centuries by some variety of others, he was the first to do so with the blessing of, and in the interests of, an actual nation-state which could follow up on his success.
The link below leads to an account of the voyage around the world begun by Magellan in 1519, written by a Portuguese who was a pilot with the expedition.
I guess it depends on what kind of significance you are looking for.
I guess if we are looking at exploration, as opposed to conquest, my choice would be Magellan who first sailed around the world (or at least one of his ships did -- my ancestors killed him in the Philippines). This is the ultimate voyage of exploration and it gives people a much better understanding of the size of the world and of the Pacific Ocean. This is very important.
The other men are very important too, but I think they "matter" less for exploration than does the Magellan expedition.