I'll conceed, "jazz" may be too broad a term. How about best ("best" as qualified in my original post) "Bebop Jazz" album.
I am not claiming that KOB is the best, as in technically or artistically above the rest in its genre. I know that there are many jazz albums of the era that surpass KOB (many of them have been mentioned in the thread above). I don't believe that any one can be considered the best as they all offer something unique.
But I like Kurt-tank's analogy with Dark Side of the Moon,(not sure about Beethoven 5th). Let me steel Tvad's term, these are "gateway" albums into their respective genres.