From a historical critical perspective, Jesus preached the kingdom of God, and Paul preached the gospel. Originally these two were different in several crucial ways. The gospel proclaimed that Jesus was the Son of God, that he died for our sins, and that he was raised from the dead. But none of these ideas were present in the authentic sayings of the historical Jesus. The kingdom of God was proclaimed to a Jewish audience, whereas the gospel was proclaimed to all people. The concept of the kingdom of God was no threat to the Jewish religion, whereas neither the theology nor the freedom inherent in the gospel could be retained within Judaism.
I think that it depends on how we define the term "gospel." If we are referring to the gospels of Matthew, Mark, Luke, and John, then obviously Jesus did not preach these types of "gospels." However, if we boil down the term "gospel" to it's true meaning of "good news" then I believe that it is accurate to say that Jesus did in fact preach the gospel, in this sense of the word. His main message was about the coming of the kingdom of God, and he brought this good news to the people of Jerusalem, in order to prepare them for the impending change. I think that the coming of the kingdom of God can be viewed as equivalent to the gospel (good news).