The proof of course is that searching in the corpus of English literature, "in my humble opinion" is found orders of magnitude more than "in my honest opinion":

The proof of course is that searching in the corpus of English literature, "in my humble opinion" is found orders of magnitude more than "in my honest opinion": https://books.google.com/ngrams/graph?content=In+my+humble+opinion%2CIn+my+honest+opinion&year_start=1700&year_end=2000&corpus=15&smoothing=3&share=&direct_url=t1%3B%2CIn%20my%20humble%20opinion%3B%2Cc0%3B.t1%3B%2CIn%20my%20honest%20opinion%3B%2Cc0 https://books.google.com/ngrams/graph?content=In+my+humble+o...