Coke > Pepsi
I think Morbid Angel was the first group I knew of to use 7 stringers. Baritone guitars are awesome, but I've never played one. I remember when Steve Vai was wanting a guitar built with 15 notes to the octave, I wonder if that ever panned out.
I don't like anything but 4-strings for bass, but for two hand tapping 6 strings or more can be quite useful.