If for example, Samsung and LG make decent Android devices and provide support for them, you could buy from them and get a decent consistant Android device and support.
If that were the case, you'd be safe. I don't know of a manufacturer that consistently provides bug-free devices and support for them for, say, 2 years back.
You are generally safe with Nexus devices, since you have the best chance of upgrading to the latest OS. This helps with vulnerabilities which won't be fixed in older versions of Android. But because Nexus devices shuffle between different manufacturers, you lack consistency from a hardware standpoint.