At the height of both bands popularity, Nirvana was definitely more successful. I also believe Nirvana sold way more albums (75+ million) despite releasing much less music. Nirvana also seems to be a much bigger deal in pop culture today. read more
Nirvana probably has more record sales than Foo Fighters, if you want to use that as a measure of success. I on the other hand prefer to use a bands performance record as a measure of success. Foo Fighters are still performing and have been for better than 20 years. read more