I have seen the JW's promote the stake rather than a cross, but also good Protestants also say it was a stake.
John 20:25 The other disciples therefore said unto him, We have seen the Lord. But he said unto them, Except I shall see in his hands the print of the nails, and put my finger into the print of the nails, and thrust my hand into his side, I will not believe.
It is of interest that nails is plural and some try to say that means Christ was nailed to a cross beam, but it is equally possible plural nails can be through the hands onto a stake.
My thought: If those crucified carried the stake then it must take the Romans some time to erect such.
If it was a cross beam (still a single piece of wood) then the tree or upright stake would already be prepared...therefore nailing the cross beam would be easier?
The cross beam could be removed and the stake left in place for the next person to suffer the same?
Watchtower literature used to have Christ on a cross, but changed later to nailed to a stake. In their books though there was only one nail through the hands, not plural!