Personally, I like having the day of the week as well, which is something the bare ISO-8601 format lacks; so my preference would be "Posted 2018-11-03 15:02 (Saturday)". In other words, user-defined? Apparently, there are currently (at least) three formats:
Posted 59m ago
Posted Saturday at 03:02 PM
Posted October 18
(I expect there to be a fourth showing the year as well).
The first one is fine with me.
The second one is confusing for me, as 03:02 implies the middle of the night (my brain is used to parsing just the time info, not the separate "PM"). This could be fixed by using the user's localization info, or even the browser's.
The third one is missing the time; sometimes it can be useful to see how much time there was between two posts in the same thread, even if they were made a long time ago. There's enough space for 15:02 (or 3:02 PM) to be added...
As for time zones, I do prefer seeing date/times in my own time zone instead of UTC.