"There are many artists that I present that I admit I like less than I do others. But I think that they warrant being presented by my own, personal standards"

Norman Granz is suggesting that although he might not personally delight in the work of some of the artists he presents, he still thinks they deserve being presented. He is suggesting that he has a particular set of requirements that he applies to the artists he picks to present, and that even if he does not personally enjoy their work, he still believes they deserve being presented. This recommends that Granz is a reasonable and objective presenter, which he is willing to put aside his own individual preferences in order to provide a wide range of artists. He is also suggesting that he has a specific level of regard for all of the artists he presents, no matter whether he personally enjoys their work.