Yes, definitely always keep your OS up to date! Even in 2017, this is still a major advantage that iPhones have over Android phones. There will be bugs in any device, and iPhones have a better plan for dealing with them than Android phones. There is a vast amount of empirical data that shows patch adoption rates are far faster on iOS.
"There is a vast amount of empirical data that shows patch adoption rates are far faster on iOS."
Is that still true for the Google reference models? The Pixel, Nexus and other references devices tend to get updates in a much timelier fashion than, say, the Galaxies, Experias, and Notes of the world, and because the reference models aren't laden with proprietary bloatware, they tend to work more reliably after upgrading as well.
A number of years ago I found a crypto flaw in a Samsung component they shipped on their Android phones. Due to carrier update delays it took nearly two years for all the patches to roll out. Apple on the other hand can go from notice to patch available in weeks.
Apple's not perfect about this stuff. Google and Apple both have strengths when it comes to systems security, including on mobile platforms.
The key advantage Apple has is vertical integration. Google has to coordinate with third party vendors to ensure that an OS patch reaches Android users. Apple can just flip a switch.
iOS patches are:
1) available, directly from the vendor
2) come with new features
3) required for certain apps
4) nag you
etc