I think you have to look at a lot of different factors to come up with a reasonable suggestion as to who is “the best.” I think the MAIN factors are:
1- musical ability, including a) singing, b) songwriting, and c) instrument playing ability.
2- How good a show did they put on live? Boston and Def Leppard put out some great LPs, but they were better in the studio than live.
3- How much did they influence the fans of their era? I mean, how many 18 year old guys saw a used electric guitar in a pawn shop window and bought it, hoping to someday play like THIS band did?
With all of the above in mind, my selections are, in order:
1- the Beatles. No surprise there. They weren’t that great live compared to some later groups, but in categories 1b) & 3 they are and probably will always be in a class by themselves.
2- Metallica. Very strong in all categories, but especially in 2 & 3. I personally know half a dozen guys who bought guitars so they could learn to play “Enter Sandman.”
3- Black Sabbath. The best combination of 1a, 1b, and 1c of any of these groups. Tony Iommi was a better guitar player than any of the Beatles or Kirk Hammet (but NOT Dave Mustaine) and Ozzy was a better singer in a lot of ways than Lennon, McCartney, or Hetfield. Their best songs (Paranoid, Iron Man, War Pigs) are as good as any the Beatles wrote.
What these bands have in common is that they either invented a form of music (thrash for Metallica) or revitalized the music scene by giving people a sound they couldn’t get anywhere else. (the Beatles, Sabbath).
There are some bands that are great even though they don’t meet my personal criteria. I think those are:
Led Zepplin. Better at playing their instruments than the Beatles, put on as good a show with less technical help than Metallica had available. “Stairway to Heaven” was to boomers what “Fade to Black” or “Enter Sandman” is to Gen X-ers.
AC/DC. So unique they’re hard to rip off. This also limits their influence. If nobody can copy them, how can anybody be influenced by them? Some have come close though.