The strong advice from multiple trusted Apple bloggers & commentators is to avoid upgrading your iPhone or iPad to iOS 13, which was released yesterday (19 Sep). There are numerous bugs in the initial release, including one major security hole which potentially exposes your entire contacts list to anyone with physical access to your device.
iOS 13.1 is scheduled for release on Tuesday 24 Sep and reportedly fixes the bugs as well as the security issue.
It is very strange that 13 was released in the condition in which it was, but unless you have a new Series 5 Apple Watch, you do not need to upgrade right now.
Useful commentary here from Daring Fireball’s John Gruber: