Samsung Galaxy S7
You might be tempted to buy the Samsung Galaxy S7, Galaxy S7 Edge, or the rugged Galaxy S7 Active. These devices are still performing pretty well in 2019, but most people are better off going with a new Galaxy S model.
It's not official, but it sure looks like the Galaxy S7, Galaxy S7 Edge, and Galaxy S7 Active will stay behind on Android Oreo. Samsung hasn't confirmed an Android Pie update and the devices haven't shown up on any recent Android Pie roadmaps.
If you want to get the One UI on a Galaxy S7, Galaxy S7 Edge, or Galaxy S7 Active, you'll need to do it manually. And a lot of people don't have the time or patience to do that.
Now, unlike the iPhone 6, iPhone 6 Plus, and iPhone SE, software support for the Galaxy S7 series hasn't completely ended.
Samsung and its carrier partners are still pushing out updates to these devices, but they've become infrequent. Bug fixes come every so often and the company is still committed to pushing out quarterly security updates. However, that will change soon.
At some point, Samsung will remove these Galaxy S7 models from its quarterly upgrade list. At that point, you'll be entirely on your own.
These devices will get upgraded to Samsung's version of Android Q, they'll get fixes and patches for the foreseeable future, and they've got better hardware. This makes them a much better choice in 2019.
On top of that, there are tons of Galaxy S10 and Galaxy S9 deals out there. You don't need to pay anywhere near full price for these devices, especially if you've got a phone in great condition. You might be able to trade it in for hundreds of dollars off the current price.
If you want to hold onto your next phone for a year or more, think about going with a newer Galaxy S model or a newer phone from another Android OEM over the Galaxy S7 series.
You probably won't regret it.