There is no such thing as "the best" in music. No best composer, no best singer, no best player, no best ensemble. Not even temporarily.
I will say that, though there are things you can judge by recordings, the LP format with its inherent sound compression and other artificial aspects will distort your experience of what the original sound that was recorded was like. Any claim that the Philadelphia Philharmonic was "the best in the world" is absurd. That would be a claim about, I'd imagine, the Eugene Ormandy era, featuring the famous "Ormandy sound". Ormandy was a competent conductor but like almost all conductors, especially those who cultivate a particular "sound" or style that is bound to work better for some pieces and composers than others.
To illustrate that here's something I'd refused to post in the past, an example of the abomination presented as "Bach's Magnificat" with the full, modern orchestra, featuring said, "Ormandy sound" and the gargantuan Mormon Tabernacle Choir singing in an abysmally unsingable English translation of the Canticle of Mary from the Latin Vulgate.
If you think that's a great recording of one of the greatest works of the Western musical repertoire, well, I can't agree.
Other violence done by the great Ormandy to Bach includes Ormandy's orchestral arrangement of the Passacaglia and Fugue in C minor, which I can't bring myself to post. It is about the polar opposite of the approach Anton Webern took in his famous analytical arrangement of the Ricercar a 6 from the Musical Offering. I'll post that.
noting that the conductor, Pierre Boulez, another fine conductor, also had his limitations. Music like that is greater than any single interpretation can capture.
I think I might have said that during part of the same period that Ormandy was conducting the Philadelphia, there were many nights I think I'd rather have been listening to the Minnesota Orchestra directed by Stanislaw Skrowaczewski.