I don't know of every instance of course, but from the general purpose ones the order of up-to-date from most to least at the time of posting would be something like: kbin.run, fedia.io, kbin.cafe, artemis.camp (specific API branch), kbin.social.

But there's also other considerations. fedia has a double post/comment issue and a low amount of 500s. Artemis has been giving me a lot of 500s, can't upvote anymore (just reloads the page), commenting doesn't always federate. Many instance admins seem to have disappeared since 3 months ago. I'm not sure what life is like on instances I'm not actively using so there might be issues unknown to me.

Edit: the keys that I look for are localization / ui changes. "more" dropdown now has "more from domain" on updated instances. The UI for the sidebar is different, and most recently the footer is differently styled. There's also the federation list of instances page in the footer now.

i update kbin.run to stay in sync with the most recent commit to the dev branch on a regular basis, although the update frequency is much lower now compared to 4 months ago... it's a "bare metal" install (no docker), so i made a very simple shell script to update it. half the time no one notices until they refresh the page or get inadvertently logged out due to a backend cache getting cleared. you're welcome to try it out if you'd like.

I used to run an instance, and one of the reasons that I stopped was there is no good way to update it. If I pulled the source code again and recompiled the Docker it just wouldn’t start. Wiped the database and it still wouldn’t start.

This is why I still tell people Kbin is not production ready.

https://kbin.melroy.org is running the latest Mbin version. Which is a fork of Kbin.