Who must we believe in to go to heaven, God or Jesus?
The answer is both. You cannot believe in one without believing in the other. "I do not pray for these alone, but also for those who will believe in Me through their word; that they all may be one, as You, Father, are in Me, and I in You; that they also may be one in Us, that the world may believe that You sent Me. And the glory which You gave Me I have given them, that they may be one just as We are one: I in them, and You in Me; that they may be made perfect in one, and that the world may know that You have sent Me, and have loved them as You have loved Me" (John 17:20-23). The Father and the Son are perfectly united in their objectives for mankind.
"He who believes in the Son of God has the witness in himself; he who does not believe God has made Him a liar, because he has not believed the testimony that God has given of His Son" (I John 5:10).
"If I do not do the works of My Father, do not believe Me; but if I do, though you do not believe Me, believe the works, that you may know and believe that the Father is in Me, and I in Him" (John 10:37-38).
"Let not your heart be troubled; you believe in God, believe also in Me" (John 14:1).