Both. All believers in Jesus who die before his Second Coming, will first be with Him in heaven, and later live with Him on the new earth, when heaven and earth will have become one.
When Jesus was dying on the cross, He told the criminal who believed in Him: “today you will be with Me in Paradise” (Luke 23:43). Paul expressed the same confidence that after death he would be with Christ: “My desire is to depart and be with Christ, for that is far better” (Philippians 1:23). So it is clear that we, if we believe, will be with Christ after we die. That is heaven, where Jesus is (see e.g. Acts 3:21), where God is (see e.g. Matthew 23:9), and where the angels are (see e.g. Matthew 22:30). The body we now have is just a ‘tent’ (2 Corinthians 5:1), and when we die we go home to be with God (2 Corinthians 5:8).
Heaven is just a half-way station
Yet being in heaven is just a half-way station. Being human is having a body. The body we now have is not that great. It has all kind of limitations. It knows sickness, deteriorates, and eventually dies. But we will get a new, glorified body on the new earth. In 1 Corinthians 15 Paul compares the body that we have now with a seed, and the new body that we will get in the resurrection with a plant. 1 Corinthians 15:42-44 reads: “What is sown is perishable; what is raised is imperishable. Sown in dishonour; raised in glory. Sown in weakness; raised in power. It is sown a natural body; it is raised a spiritual body. If there is a natural body, there is also a spiritual body”.
Resurrection of our bodies
Jesus’ teaching and what we read about the resurrection body of the Lord Jesus give us some idea about how our resurrection bodies will be. We can still eat (Luke 24:43), we will drink wine with Jesus (Matthew 26:29). We will not be married (Matthew 22:30). Some of the limitations of movement will disappear, as Jesus showed by appearing in a closed room (Luke 24:36) and by suddenly disappearing (Luke 24:31).
The Bible talks a lot more about the resurrection of the dead as our hope for the future (e.g. Romans 6:5, Philippians 3:11), than about our being in heaven. The resurrection of the dead is part of the Gospel message (e.g. Acts 4:2), not our going to heaven.
After the Last Judgment, there will be a new heaven and a new earth where we will live with our new bodies. The heavenly Jerusalem will come down from heaven and be on earth. God the Father and God the Son will be there (see Revelation 21). Heaven and earth have become one. Heaven has come to earth. But because when we use the word ‘heaven’ normally we do not think about dirt, trees, and rivers, it is best to use the term ‘new earth’ for the place where we will spend eternity with God.