It's clear I'm outvoted, but every now and then I use shorteners here and would miss them.
Some URLs are very long and, when linking something in a comment (say, a page from a book), they can really be an annoyance.
So I'd suggest that: If shorteners are banned, then make urls not count towards the character limit in comments.
There’s no difference for the person clicking the link, but there are minor differences for the person posting it, and for a hypothetical person who might read the URL but not click.
The magic number that’s common in your two examples, 13855, is the database identifier of your post. When you visit a link of the first form, your browser is redirected to a ...
Presumably$^1$ not, but it is most safe to use the permalink format suggested when clicking the share button.
It sometimes makes a difference if the URL contains extra stuff (e.g. accidentally linking to a specific comment if the intent was to link to the question itself).
$^1$ The word presumably because SE presumably will make sure that links work in ...