The manner of his death is of less importance than why he died. But since you asked.
I believe that the evidence of the Bible shows that it was probably a cross.
*** Rbi8 John 20:25 ***
25 Consequently the other disciples would say to him: "We have seen the Lord!" But he said to them: "Unless I see in his hands the print of the nails and stick my finger into the print of the nails and stick my hand into his side, I will certainly not believe."
*** Rbi8 Matthew 27:37 ***
37 Also, they posted above his head the charge against him, in writing: "This is Jesus the King of the Jews."
If his hands were above his head, then the scripture would have read, "above his hands" as the place for the notice.
Loris