This is an interesting question. I think how you choose your next console is mostly based on your past. Or maybe you are no serious gamer of any kind and just want to splash into the gaming realm your own special way. I put a lot of thought into this post, so here goes...
That said... I mostly will want to choose based on what console I can realistically see myself taking advantage of for a long time to come. Choosing a console should be like buying a car or buying a house- you want something that will last and that you can make the most of for a long time. I seriously loathe the concept of buying one console for just one game or one certain feature. Even when you buy a system that ultimately fails (for example: the OUYA, and I am an unapologetic OUYA owner), you want to make the most of what you buy instead of just using it for only a few features. You'd rather make the most of something for as long as a system's shelf life allows than here-and-there usage without really taking advantage of it.
The only option closest to my thoughts on getting a next-gen console is "the best exclusive games." Honestly, my option is somewhere between "the best exclusive games" and "based on my current console." I selected exclusive games because I think exclusive titles are what makes your console a seller. Think of all the people who'll play Nintendo systems mostly to play the likes of Mario, Zelda, Kirby, and others. In addition to the stats and figures on any system, the proper set of games help sell your game system. I think of exclusive games more like how racing/driving games have certain tracks and cars to them. Some people dislike fictional vehicles and fictional locations, but they do have an advantage in providing a unique aspect and identity to a game. Same goes for exclusive titles for systems, including
Now to discuss the "current console" aspect. I keep contemplating about getting a PlayStation 4 as a PlayStation 3 owner. Then you have the PlayStation 5 talk, and I keep thinking if I should save up for the PS5 or at least get a used PS4 from GameStop or someplace. Really, I am torn between getting a PlayStation 4 or a Nintendo Switch. Even if the Switch is not as loved as any PlayStation or any XBOX, there are people who actually play and love the Switch. So don't give me the notion that the Switch is not a favorable option in this context. In today's gaming culture, game consoles are not just "game consoles." They have applications and stuff outside of physical and digital games. For example- YouTube and Netflix apps. There's a lot to consider when going to a newer console, and you have to weigh your options properly.
So to the "TL;DR" crowd, my option is on choosing a new console based on exclusive games. I would say in upgrading from a current console, but I took into account if you are not going on past consoles. That's why my decision is on exclusive games more so than upgrading, though upgrading from previous consoles is a factor in choosing a new console.