Technically, Gandalf's biggest fight was probably during the last battles of Beleriand, where the Maiar were instructed to destroy Angband and restrain Melkor. Gandalf may kill Durin's Bane, but he also dies (and is sent back by the Valar). His power requires that a staff be used, as compared to Yoda, whose skills are always there; he only uses a Lightsaber to defend himself against another Lightsaber.

Yoda gets to fight Palpatine, but he also dies of natural causes, and despite that, he can still exist because of Qui Gonn's revelations. In this case, the Force would overpower Gandalf's abilities, since in both the movies and the books, his ability to use Magic is restrained by the Valar, not that he uses it at any other point in his history, since Magic as we know it does not technically exist in M-E. However, as a celestial spirit, the powers of Gandalf are as of yet, unknown in their fullest.

But Raoul Duke would pwn the both of them, simply because he speaks for the author and voices his opinions, rather than being a tool of the author.