I've sometimes said that this is like asking which wing of an airplane is more important! Both are equally important, and both are equally essential.
Jesus' death on the cross is important because without it we would have no hope of forgiveness or eternal life. Only one thing will keep us out of heaven, and that is our sin. Sin is an offense to God, because it's like telling Him that we don't want anything to do with Him. And because of this, sin cuts us off from God -- both now, and in eternity.
But on the cross all our sins were laid on Christ, and He became the final and perfect sacrifice for our sins. We deserve to die and be cut off from God forever because of our sins -- but by His death on the cross Christ took upon Himself the judgment and Hell that we deserve. As the Bible says, "God made him who had no sin to be sin for us" (2 Corinthians 5:21). Because of the cross we can be forgiven!
Equally important, however, is the resurrection -- for by it Jesus proved that He was the Son of God who could take away our sins. More than that, by His resurrection He conquered death and Hell and Satan for us. Now we don't need to fear death, because He has defeated its power over us! Jesus' promise is for you: "I am the resurrection and the life. He who believes in me will live, even though he dies" (John 11:25). Is your faith and trust in Him?