I would go with Annihilus because of the extras. Black Adam is Black Adam and during WW3 it was said that there were stronger, faster and even overall more powerful beings on the battlefield, but no one was as ruthless as he was.
Black Adam faced a bunch of heroes, who tried to stop him. I can imagine that no one ever tried to take him down once and for all. Heroes often go easy on the villains, since they're basically heroes.
Annihilus won't have such moral issues, he would go out. And I see him being more powerful then Black Adam if he wields the cosmic control rod and the bands.