Nirvana, most definitely!
Pearl Jam was popular for a longer period of time than Soundgarden.
Soundgarden, Mother Love Bone and Pearl Jam are considered some of the most popular grunge bands. However, the actual most popular grunge band before Nirvana is to ones own opinion.
They are both considered grunge bands
Nirvana
Green Day, Nirvana, Blur, Oasis, and Soundgarden should have been but was overshadowed by Nirvana.
Nirvana
Nirvana
Nirvana
Stone Temple Pilots
Guns N' Roses
Red Hot Chili Peppers
Seattle Four