Best is way too subjective of a term to ever come up with a definitive answer. The closest you will ever come to a consensus (or even a quorum) on this question will be the Beatles. The reason for that is, like them or not, they practically invented most everything in rock and roll as we know it today. Before them, bands didn’t even write their own material and the majority of rock and roll was formulaic, based solely on what had worked in the past. What the Beatles managed to do was to work collaboratively to create new approaches to songwriting and tunesmanship. They were able to figure out the basic “hook” of popular songwriting…that sound which just grabs a mass audience and won’t let go, but to take that hook an interpret it in a way that hadn’t really been thought of before, so that the sound had more of an edge to it, they gave rock and roll teeth essentially. And once they created one sound, they did not stick with the formula…with each album they branched out a little bit more and created this catalogue of brilliant pop music with a harder edge which utilized elements which had been around forever like melody and harmony, but gave it a unique polish which had really never been seen before. They became the band that everyone had to sound like, but as soon as someone would copy their sound, they would change it up. Then in the mid 60s, they began “opening their minds” with hallucinogenic drugs, eastern philosophy, and perhaps most importantly, via a meeting with Bob Dylan who told them that they were great and unique and irreplacable, but that they didn’t say a goddamn thing. After that, their music began to take on depths that no popular music had done before, it began to carry some importance, some gravity, and the experimentation with sounds went off the charts. Each album was not, as it had been in the early 60s, a slightly new take on their previous theme, but a complete reinvention, a milestone in musical evolution. Basically they paved the way for the hippie/love era, they paved the way for the bombastic metal, they paved the way for the alternative music of today. In just about any music that exists you can hear if not a direct Beatles influence, then an indirect influence, via a clear influence of someone who WAS influenced by the Beatles. If the Beatles hadn’t come along, rock and roll would NOT be anything like it is today. So, as I define “best”, I have to look towards “influential” as my criteria, and I have to say the Beatles is the only answer that actually makes any sense to this question.
Now, two more times in rock and roll history I feel a band has cast a shadow ALMOST as large as the Beatles, but neither quite managed to do what they did. First was Black Sabbath, who themselves wanted to BE the Beatles circa 1966. They essentially put the heavy in heavy metal…no band was as heavy, as dark, as bombastic as they were. Think about 1969, you usually think about hippie dippie Crosby Stills and Nash kind of folky c’mon people now, smile on your brother kinda music. But Sabbath was putting out music that sounded like Satan himself had written it…this music just came out of left field and defined the entire metal culture. Some mention Zeppelin as heavy metal pioneers, but really what Zeppelin contributed in the long run was three things…one was taking what was old and making it new…most of their early inspiration came from old school rhythm & blues, two was guitar virtuousity, and three was the falsetto that would a decade and a half later become the staple for hair metal, a really poppy offshoot of what Sabbath started.
Not until Nirvana did we have another band that really shook the very foundations of rock and roll, and just like everyone before them, they did it by taking old ideas and making them new, building upon them. From the late 70s until the late 80s, rock music branched off in a number of different directions, and much of what was put out there really had no pop connection, there was no hook, nothing to connect to a mass audience, and that music went underground. Kurt Cobain was an afficianado of so much of this music which really was groundbreaking and extraordinarily unique, the culmination of years of people thinking outside the box, and he took those ideas and crafted them with a real songwriter’s sensibility, making them (much of which was considered “punk”) far more accessible to a casual listener. Their legacy could have possibly ended up being greater than that of the Beatles had they lasted more than 4 albums, but each album was a sea change from the last, much like what the Beatles accomplished (and really no one else of any import) in the 2nd half of THEIR career. Nirvana expanded creativity to the mainstream which was stuck in the doldrums, listening to the same recycled music they’d been listening to forever.
Each of those three bands changed the collective musical sensibilities of the youth culture and cast a shadow that will be felt no matter how long rock and roll lives. But the Beatles were the first, the longest lived, the most widely varied and cast the greatest and longest lasting influence.
Now, if you want to use a different criteria for best rock and roll band ever, I have one other I can suggest. Rock and roll music is essentially at it’s core about sex, about animalistic rhythms, driving beats, just balls out good times, party music that makes you feel like beating up midgets. what do you mean, that’s just me? Seriously though, it’s just about an unrelenting assault on your senses that is simultaneously energizing, familiar and with which one is compelled to sing/dance along. It’s about partying hard and feeling alive. For my money, no one has as consistently for as long been true to that definition of rock and roll as AC/DC. They are an unapologetic rock and roll band…they’re songs don’t say anything and they don’t give a shit. You put on Back in Black and it’s impossible to sit still.
There’s my 2 cents (or in my case, buck fifty).