I've seen a lot of great bands at the beginning and peak or their careers, but the Clash eclipsed almost all of them (when they were on their game anyway, which appears to have been about a third of the time).
Better than Aerosmith third on the bill with one record out and everything to prove, better than Bob Dylan in 1978 with nothing to prove, but still kicking ass, better than Iggy Pop in a bar room that held maybe 300 people, better than Led Zeppelin two nights in a row (almost got killed that second night, but that's another story), better than Bachman Turner Overdrive - wait, scratch that last one...when the Clash were good there was no one better.
Well, except the Bad Brains.