This, a well FF have had a great career of making quality modern rock-esque music. Nirvana has always been that "grungy rock band with the pessimistic, whiny singer" for me.
I respect Nirvana I just don't listen to them much expect for a few songs. I am sure if I grew up with the band that statement might be different. Foo Fighters are one of the last beacons of modern rock n' roll in age on generic pop music and party anthems. Both bands deserve credit for there art but yea I find FF a bit more engaging to listen to.
That being said it does suck Kurt Died regardless of what happened anyways. He may of been a famous singer and lived the rock lifestyle but he was only human.