Apparently alternative just means "mainstream 90's rock." Which, actually, was what I understood it to refer to at the time. The style that grunge/alternative was supposed to be a counterpoint to (i.e., butt rock and hair metal) had all but disappeared by the time Smells Like Teen Spirit came out, so the "alternative" label never made any sense as a literal description. In much the same way, I expect that "indy rock" will ultimately end up meaning simply "2000's mainstream rock." Anyway, to the topic: the best 90's rock was Nirvana's Unplugged album. They subverted many of the by-then-already-tacky grunge categories that they were themselves leading exemplars of, broadened the standard alternative cannon outside of tired punk puritansim with all the Meat Puppets and David Bowie covers, and managed a profound connection with the audience in the process. And they did all that live.