I very much doubt that even all the 9 Nazgul together would be stronger than Gandalf...especially Gandalf the White...since he is a Maia (despite being in the mortal frame) AND he has Narya that Cirdan gave him....
The Nazgul were only wraiths and Glorfindel nor any of the high elves were afraid of them because as Legolas himself said, those who had lived in the Blessed Realm dint fear them (wraiths) and they had great power over both the Seen and the Unseen.....Gandalf would definitely count under more than just "lived" in the Blessed Realm.....The Nazgul's power is just so feared because its stems from Sauron himself....
But since no such standoff actually takes place in any of the books, there will never be conclusive evidence of the fact...although considering he fought off five Nazgul alone at night when they are strongest, when he was just Gandalf the Grey would atleast give some measure of his strength.....
Also about Ungoliant yeah.....she was exceptionally powerful....someone who can bring down the most powerful Vala like Melkor to the level of screaming for help, thats wickedly powerful....
I think the OP meant Fingolfin who apparently did fight balrogs since he had sieged Angband and even wounded Morgoth seven times in a duel....even Morgoth feared him....