"Better credit rating" unfortunately is too broad of a question. The possible gains in a numerical FICO score will simply be too minimal to do your study! Comparing low utilization of 1-2% vs 0% for differences are problematic, as the utilization factor - which is empirically known - stops having a meaningful effect on your scores below 10%. At least in a way that would alter anybody's behavior.
As such, you will not find empirical evidence for this argument (outside of Fair Isaac saying so themselves).
Now you did ask specifically about credit rating, which I should point out is different than credit score.
You do not need to spend any money to achieve a higher credit score. So there is your 0% answer. A credit rating on the other hand, includes spending behaviors that make an institution more likely to extend credit.
An institution is more likely to extend additional credit if they have seen utilization of their credit based financial products. An institution is less likely to extend additional credit if they see 0% utilization on their credit based financial products. An institution is more likely to close your credit based account if they see 0% utilization. Your credit rating - with that institution - is now lower, without any affect on your credit score.
BUT, by having a line of credit unilaterally closed by the institution, now your credit score becomes affected due to possibly lowered Average Age of Accounts, and lower amount of overall credit (increasing the utilization % that you have across other credit lines). This part isn't "rational", it is cause and effect.
So you want to avoid making situations where your credit lines get cancelled. Having 0% utilization is one of those exact situations.
If this wasn't satisfactory, due to lack of sources, just make a note of which paragraphs you want citations for.