Jonathon Edwards preached "fire and brimstone" messages, in which he told his audience that they were all going to Hell if they didn't repent. He seemed to focus on the negative side of salvation. He is best remembered for "Sinners In the Hands of an Angry God", which says that God is dangling humans over the fieriness of Hell like we would to a spider.
George Whitefield preached "nicer" messages, stating that God is good and loves us all. The audience was more used to this kind of preaching.