Realistically Hirohito had very little practical power. Japan was a de jure Constitutional monarchy, but Hirohito wielded more power than a constitutional monarchy probably should. He was supposed to ratify any decisions made by the council and prime minister, but in reality he often quarrelled with them and usually had to be convinced. An example would be Hirohito's opposition to the tripartite pact. Hirohito also had issues with the war in china since it was dragging on longer than expected. Hirohito was also in charge of appointing prime ministers (Tojo was picked because he was deemed to be loyal to the imperial office). Hirohito also got much of his power and influence from the fact that he was seen as a god, and any official seen directly opposing him would be in serious trouble.

Source: Imperial Japanese army it's rise and fall by Edward drea

Trying to ascertain the relative power of a particular individual in the Japanese wartime government is not a very useful exercise. The structure of the government did not allow individuals to exercise much power without first securing the backing of their relative ministries, and then building consensus among the cabinet and Supreme War Council. To understand the motive forces of Japan's wartime actions, you need to look at the the rivalries between various branches of the government and military, as well as the negotiations between them.

Tojo's career shows that he was not a particularly bold leader, and was more of an effective army bureaucrat than anything else. His policies were generally the policies that the Army General Staff decided on and passed up to him. He would then dutifully go about implementing the policies that were decided for him. The postwar portrayal of Tōjō as some kind of mastermind, reinforced by the prosecution's narrative at the Tokyo War Crimes Trial, is more or less mistaken.

Similarly, Hirohito served as a rubber stamper, approving what the Cabinet and Supreme War council told him to approve. He tends to get credit for the decision to surrender in the popular narrative, but his decision to surrender can also be viewed as the result of successful lobbying by the peace party within the Supreme War Council. See this thread for a more in-depth look at the decision to surrender

That is not to say that nobody was responsible, but the main idea is that policy was generally decided on by the officers of the army and navy general staffs, and merely carried out by the supposed leaders.

If I had to answer the question either way, I would say Tōjō had more power, as his actions in the cabinet actually did influence the outcomes of the negotiations between the Army and Navy, whereas Hirohito rarely entered into those debates until after they were concluded. On the other hand, /u/Warband14 makes a good point in bringing up the the fact that ministers often had to cajole Hirohito and negotiate with him to get his stamp of approval. Long story short, the structure of the Japanese government put decision making power in the hands of bureaucracies and ministries, rather than in the individuals that headed them. That makes questions about individual power extremely difficult to answer.