We all know there are lots of shitty wp plugins. This thread, however, should focus on those that you have used yourself and can recommend whole heartedly
The ones I can think of are:
Updraft Free for scheduled Backups.
AIO WP Migration for one click backup&restore of wp Installations. There are numerous ways how to increase the maximum import size without having to pay as it’s easily hackable in a single code file. Don’t get me wrong. I don’t mind paying for plugins I like but this single feature is easily editable in a file.
Divi Builder: ElegantThemes Divi Theme&Builder is a great bang for the buck and comes with lots of premade layouts
WP Server Info Shows some nice info.
W3 Total Cache Caching.
PHP Compability Checker Just works.