In a work as long as and complex as Dante's Divine Comedy, there will be differences of opinion. However, it does appear Virgil is the greater hero for several reasons.
First, we need to realize that Dante's world is a Christian world. For this reason it is very odd that Virgil is Dante's guide. In other words, the pagan Virgil is a guide to the Christian Dante. This alone shows that there is a heroic quality that Virgil possess.
Second, Virgil symbolizes and quality that was becoming more and more prized, reason. In fact, Virgil is characterized as the pinnacle of human rationality. This is why he is Dante's guide through hell and purgatory. For example, Virgil seems to know everything. He knows to throw dirt in Cerberus' face to bypass him; he also knows to call Geryon to get a ride. In short, he is the guide par excellence.
Third, Dante says these words to Virgil, when he first meets him:
"O light and honor of all other poets, may my long study and the intense love that made me search your volume serve me now. You are my master and my author"(Inf. I 82-85).
From these words alone, we can see that who the hero really is, at least according to Dante's opinion.