Samsung is undoubtedly the king of software updates in the land of Android phones. For the longest time the company guaranteed two major OS updates to devices across all price points, and now, Samsung promises three generations of OS updates to many mid-range devices and all flagship phones. Security updates, meanwhile, are guaranteed for as long as four years, and up to five years for some enterprise edition variants.
It's not Apple-grade, but Samsung's software support game is far ahead of the rest of the competition, especially given the number of devices it spits out each year. Some manufacturers, like OnePlus, are trying to bridge the gap in some ways, but others aren't so concerned. Case in point: Sony's new flagship, the $1,299 Xperia I III, will be supported “with the latest Android updates for two years after its launch.”
Even the Galaxy A51 will get more big OS upgrades than the Xperia 1 III
That's right: A Sony phone that is competing with the Galaxy S21 Ultra, Samsung's top-of-the-line flagship, is being promised lesser support than what Samsung's mid-range Galaxy A51 will manage. And Sony isn't even saying anything about security updates. Those are arguably more important in this day and age, but only Samsung seems completely sure about its intentions and long-term plans as far as security updates are concerned.
At the end of the day, if post-purchase peace of mind is an important parameter for you, Samsung's phones are pretty much the best you can get. Not that Samsung can rest on its laurels, because at least one manufacturer — the maker of Android itself — is reportedly trying to destroy the Korean giant's software update advantage by promising five years of support for upcoming Pixel phones, though it's unclear at this time if that support will translate to five Android OS updates.