Google's John Mueller said on Twitter that the order of the URLs in your XML Sitemap files does not matter. He did say that you probably should save the "start of the file for the most awesome URLs." But he later added that "the order among them doesn't matter." He then clarified to make it clear "the order in the sitemap file doesn't matter at all." He said the awesome comment was that your web pages should be awesome in general.
Here is his tweet:
Save the start of the file for the most awesome URLs -- the order among them doesn't matter. Ideally, that covers your whole site already, so you're all set!
— John ☆.o(≧▽≦)o.☆ (@JohnMu) June 13, 2018
Vanessa Fox responded on Twitter as follows:
Yes, John - tell us more! Why put the most awesome URLs at the beginning of the file? (That can be difficult to with programmatic files generated for large sites, but also, you know that will lead to the mad dash trying to figure out how many Google considers the "start" part. :)
— Vanessa Fox (@vanessafox) June 14, 2018
John clarified as explained above:
I see my nuance didn't make it across :). Your site should be full of most awesome URLs -- the order in the sitemap file doesn't matter at all.
— John ☆.o(≧▽≦)o.☆ (@JohnMu) June 14, 2018
Forum discussion at Twitter.