I upgrade every two years, usually in summer after bugs get fixed or at least assessed. I don't stay on older releases because it gets progressively harder to install new versions of software. Example from a few days ago, OSM for emacs requires an emacs version newer than the one in 20.04. There are ways to install it but it takes time.
Same here. If it comes out in April I usually wait 2-3 months and then upgrade, unless there are severe reasons not to (e.g. it's a work machine and we're running some weird stuff where I'd be the one doing all the work to make it run on the next one), or if I have actual problems with the old one, only then I'll go first in April. Does not apply for my random "browse some stuff at home" laptop, there would be no reservations going ahead on release day.
my headless home server is the same, every other summer a few weeks after the .1 release, i suck it up and update. usually after a few hours i have all my crap up and running again.
im hoping for a smooth update this summer as ive migrated a whole bunch of stuff over to docker.
And 18.04 will be EOL next year, right?