NMA is my favourite band, yes. I would put that down to longevity. There have been other bands in the past who I would have said were one of my favourites, but the short list has always included NMA. None of my other favourite bands have delivered as many albums to keep them up there.
Who knows, if Nirvana did not end the way it did, and carried on with follow up great albums, maybe they would be a rival, but beyond all the personal attachment to the band I feel, and a band I go to see, there has been a constant stream of fine quality albums, and still hopefully more to come.
Most of my other favourite bands are long gone. Doors, Hendrix, Pistols, Nirvana, Generation-X, etc. etc.