Yep I think Soundgarden is far superior then both.
Matt Cameron is a great drummer, even though he played w Pearl Jam for awhile.
Nirvana really sucked. One of the worst bass players I've ever heard...right up there with Duff McKagan
I never felt that PJ took advantage of Cameron's playing; especially the ease with which he seemed to "mask" a lot of odd time signatures used during his Soundgarden years. Cameron w/ PJ felt like someone driving a Ferrari in the slow lane.
Nirvana didn't do much for me. However, I think it was the timing (similar to when Punk "dethroned" large area rock acts), with Nirvana making the Motley Crue's of the world look silly and outdated, that created their legacy. Plus, and I'm sure I'll get some stones thrown for this, Cobain's death cemented him along the lines of Morrison, Hendrix, and Joplin; a tortured artist that created so much "great" stuff. If he hadn't died, what would Nirvana have been by 2000? 2002? 2004? I don't think they'd be considered as "important". Sorry for the tangent.