The OnePlus 3 and 3T are now about 3 years old. Despite this, they are still receiving new software updates from their OEM. The latest of these include new security patches for Android 9.0 (Pie). The same can be said for their predecessors, the 5 and 6 lines.
https://www.notebookcheck.net/OnePlus-upgrades-its-2016-8-phones-to-August-2019-security-patches.428917.0.html
QuoteThe OnePlus 3 and 3T are now about 3 years old. Despite this, they are still receiving new software updates from their OEM.
I recently switched to Apple after getting burnt by Samsung and LG dropping software support for devices that were still pretty relevant hardware wise...
A Pixel device may have sufficed too, but Apple has had a pretty good track record with keeping iPhones (even older ones) updated.