My impulse is to say the 70's "overall".... However, after seeing many of the greats live including VH, AC/DC, Page, ect.... The best live guitar tone I've heard by a wiiiiiiiiiiiiiiiiiiiiiiiiiiiide margin was Dean Deleo of Stone Temple Pilots. Nothing even begins to come close to his Demeter / AC30 rig and the amounts of clarity that he gets while using the unique driven sounds from the Demeter. The AC30 isn't actually required for most of the clarity, the Demeter provides most of that while a Marshall or Mesa would be considerably more reliant on the 2nd amp to hold down the fort on the clarity front. Not to mention the most unique use of modulation I've ever heard. The relationship between that Demeter and the Intelliverb is a very special thing when you start using chorus for just the right amounts of texture the way he does. This one dude is so good in his own right I had to vote 90's, sorry 70's.