What advantage do you see of the ATV3 over the ATV4 that would inspire you to go back?
A few were mentioned already in this thread, but I will list some things. A lot of the things maybe subjective, and based off of my experience, while others are well documented issues with the ATV4.
1.
The ATV3 doesn't have the bugs that the ATV4 has. With every tvOS update it seems like for every one bug fixed, two more replace it. I restart my ATV4 almost everyday, something I rarely ever had to do with the ATV3.
Some of these bugs maybe app related, but the ATV3 version of these apps do not have these bugs.
2.
The Apps are much better on the ATV3. The App store is probably the biggest selling point of the ATV4, but so far, there hasn't been any must-have apps available from the ATV4, that are not available on the ATV3. At least for me, the apps my family uses most on the ATV4, and already installed on the ATV3.
The UI on these apps are much better designed. Trying to browse stuff to watch on Netflix on the new ATV4 is a PITA. The ATV3 version is much easier to navigate and use.
I think the ATV4 versions look nicer at first, until you try to use them.
3.
The remote. Using the remote has not been a great experience. Accidentally hitting the wrong button, holding it the wrong way, and the (sometimes) long wait for it to pair, makes using the remote a pain.
I prefer to use IR remotes, but the programmed IR buttons are inconsistent between apps, and limited when you need to force close an app when it stops working properly. Which having to force close an app is an everyday occurrence especially with the YouTube app.
Also, trying to play most games with the Apple remote is frustrating. I downloaded some games that I already own and played thinking they would be fun, but the remote made them almost impossible to play. DuckTails is one example.
4.
Lack of good apps. I would probably keep the ATV4 on my main TV if there were some decent apps that I liked. I was hoping for Amazon, which was rumored to be released last December and that never happened. The games are nerfed by the Apple remote requirement. All the best video apps on the ATV4 are also on the ATV3.
5.
Having a user friendly UI. The ATV3 UI is very simple and easy to use. My baby-boomer parents learned how to use it and are happy with it. The hardest part for them, was how to re-authenticate the cable subscription for channels like HBO.
I was planning on buying them an ATV4 for x-mas last year, but quickly changed my mind after using mine. I knew that if I would replace their ATV3, I would either get calls from them constantly asking how to do stuff, or they would get frustrated with it and never use the device.
There are other issues, I could go into more detail about the bugs, but I think I made my point.