In evaluating any work, it is useful to note its distinctives, if any. What are the distinctives of the book described as 'the King James Bible'? It certainly has several of them- which may or may not be considered qualifications for the title' 'Best Bible'. Alternatively, it may be considered to be obsolete-what many British Christians described as 'the steam Bible' in the days when steam railway engines were being replaced by diesel locomotives.
a) It is the only translation of the Bible that has no proper name. It was never described as the 'King James' until comparatively recently, and that mainly because the previous name for it was found to be either inaccurate or embarrassing. This book was never authorised for general use by any monarch or Parliament. In the USA, the country in which the 'KJV' is most used, one can hardly use the epithet 'authorised' because many of the settlers of the USA were escaping the authority of James (and indeed could still be said to be in rebellion against the British Crown).
b) It is the only translation used and presumably approved by those who oppose or are skeptical of Christianity- humanists, atheists and the press.
c) It is the only English translation in common use that retains archaism, that many people find a strong disincentive to reading. (In Britain, it is no longer in common use in book form by actual readers. There are very few other than humanists, atheists and the press who use it, and they, one may presume, mostly in electronic form. British evangelicals who use it (except for Strong's numbers) are very hard to find, and probably of very great age.)
d) Before publication of the NKJV, it was the only English translation in common use to be based on Greek manuscripts now believed by the majority of scholars to be more or less unreliable, though of course the advocates of this translation dispute their view. It is certainly still the only one to fail to take advantage of the considerable advances in scholarship, that nobody disputes, in every relevant discipline. Even the translators of the NKJV, realising the need to modernise, expressed their misgivings about a repeat use of the same source text used in the 'KJV', but presumably accepted, along with the publisher, that sales would be seriously affected if a more modern source text was used.
e) It is the only translation of the Bible in common use that contains passages or renderings that are of doubtful provenance without indication of the doubt. In particular, the Comma Johannaeum, that some have used to justify trinitarianism (though the Comma does not actually do that), is retained after four hundred years, despite clear evidence that it was a spurious modern addition of the second millennium. The 'KJV' translators knew of this doubt, but included it.
f) It is the only translation (afaik) made by considerable numbers of people who were never paid for their work. This may indeed be a measure of justice, because there is very sparse evidence that many of the translators knew much about the source languages of Greek, Hebrew and Aramaic. (Curiously, over fifty detailed records of the proceedings of translators were made, but only one of them has survived- and that arguably hints at a low level of knowledge of source languages.)
g) The 'Authorised Bible' was the only Bible other than the Vulgate to be the only Bible in common use for hundreds of years, even though there were significant advances in availability of texts and of much greater understanding of Greek in this period; though evangelicals used it only as a start point, and went to Greek and Hebrew for exegesis, a phenomenon that has (regrettably, in the eyes of some) diminished because of the use of more accessible and up-to-date versions. It could be that the 'Authorised' was 'the best' because it was 'the worst' (though there was no real choice), and drove those who wanted to know what the Bible actually said to use of source languages.