Well, Gandalf defeated a Balrog in Moria, and Gandalf (Olorin) would presumably still be able to change physical form upon his return to Aman, I would say that Gandalf was more powerful. The Istari were probably more powerful than Balrogs, since Balrogs went under the dominion of Morgoth long ago.
__________________
...where the instrument of intelligence is added to brute power and evil will, mankind is powerless in its own defence.
|