@WizardWarrior1 I am not insulting you. I am aware of what you are saying. I just wanted to make a joke. No offense.
But yeah, power and strength are synonyms in basic English language. But in more advanced perspective and in power-scaling, strength is a single component of one's power. I still believe Ungoliant is the most powerful of this group, thus meaning she will probably win. It took all the Balrogs to defeat her, so just one of the weaker Balrogs would certainly be killed. Furthermore, the Blue Wizards both were not of Saruman's power, so neither of them could slay the Witch King of Angmar. I doubt the Witch King could kill Ungoliant or Anacalagon. Between the two, they both have insane levels of armor, strength and mobility. If Anacalagon plays his cards right, he'll definitely win. But Anacalagon is surely less durable than Morgoth, so if it got in close range, she would eat him.