What are the important traits that Blackie and Trevor have throughout the story?
We are given less information about Blackie, but we know that he was the leader of the Wormsley Common Gang. As such he has clear leadership potential, but interestingly, he doesn't seem to mind when Trevor seizes the leadership so long as the fame of the gang will spread, although he was aware of the "fickleness of favour":
Driven by the pure, simple, and altruistic ambition of fame for the gang, Blackie came back to where T. stood in the shadow of Misery's wall.
Likewise we see later on that when Trevor's leadership shakes, Blackie is there to back him up and stick with the plan.
Trevor, on the other hand, seems to be a much more complex, and disturbed character. Note the following description of Trevor as he reveals his plan to the gang:
T. raised his eyes, as gray and disturbed as the drab August day.
This focus on his eyes clearly indicates there is some psychological issue with Trevor that has resulted in his nihilism. However, he is able to lead well and give clear directions:
T. was giving orders with decision: It was as though this plan had been with him all his life...
He also shows that he can think quickly to overcome the problem of Old Misery's return. However, the defining characteristic of Trevor seems to be his detachment - he neither hates nor loves and his destruction is done without passion:
"All this hate and love," he said, "it's soft, it's hooey. There's only things, Blackie," and he looked round the room crowded with the unfamiliar shadows of half things, broken things, former things.
Therefore Trevor is clearly the more disturbed boy, when we compare both Trevor and Blackie.