This is one of those questions I utterly hate because (a) I enjoy such a ridiculous range of music, and (b) many of the bands I'm into most people haven't heard of.
Overall though, I think I'd have to say Coil
, who's range of texture, versatility, and sonic experimentation I've yet to find matched by any other band. The nucleus members were also an openly gay couple who were pro-choice on all fronts. They collaborated with many well known fringe and experiment musicians and were part of the burgeoning industrial movement scene in Europe. If you haven't guessed by now - my tastes are decidedly not usually commercial.
For lyrical and melodic writing, it would have to be a toss up between Joni Mitchel and the Beatles.