What is your preference? And if you’re a client and are now realizing that your website was built with two spaces and you’d prefer a single space between sentences, or vice-versa, please just send us an email so that we can make the necessary adjustments.
Personally, I’m not sure which is better, I just enjoy watching people argue about it. From my angle, this is a generational thing. I attended grade school in the 90's and early 2000's and two spaces after a sentence was standard at the time.