Here we are:
Archimedes, Newton, and Gauss, these three, are in a class by themselves among the great mathematicians, and it is not for ordinary mortals to attempt to range them in order of merit.
-- E.T. Bell, Men of Mathematics (1937); p. 218

Did Newton or Leibnitz either one actually develop the fundamental theorems of calculus?
This is the fundamental theorem of the calculus as it presented itself to Newton and independently also to Leibniz.
[¶] Later, in 1712, .. the question as to who had invented the calculus became a matter of acute national jealousy, and all educated England rallied behind its somewhat bewildered champion, howling that his rival was a thief and a liar.
Newton at first was not to blame. Nor was Leibniz. But ... Newton acquiesced in the disgraceful attack and himself suggested or consented to shady schemes of downright dishonesty designed to win the international championship at any cost -- even that of national honor. Leibbniz and his backers did likewise. The upshot of it all was that the obstinate British practically rotted mathematically for all of a century after Newton's death, while the more progressive Swiss and French, following the lead of Leibniz, and developing his incomparably better way of merely writing the calculus, perfected the subject and made it the simple, easily applied implement or research that Newton's immediate successors should have had the honor of making it. Id., pp. 103, 113-114 (1st emph. added; 2nd in orig.)