There are two things you should keep in mind when setting up a backup plugin.
(1) You install a backup plugin the minute your site is up and running
(2) Always, always test the backup created by the plugin and see if you can restore your site correctly with everything intact.
If you’re working as a developer, I highly recommend Backupwordpress. An absolutely non-fussy backup plugin. Just plug and play.
For non-tech savvy users, I recommend something like UpdraftPlus. Backupbuddy is good too but it takes up wayy too much memory and a lot of webhosts have banned it anyways.