Mudhoney. Period. Mudhoney basically is Grunge itself. As the best grunge band, Mudhoney blows Nirvana out of the water, damn they rock so hard. Mudhoney did not create grunge though. Neither did Nirvana or The Melvins, like the other people said. Malfunkshun created grunge, so be thankful, people.
The Grungiest song ever is "Thirteenth Floor Opening" by Mudhoney. The sound is so dirty in that song. I love Grunge.