If you were to list the best games of this generation, almost all of them are on PS4. By not buying a PS4, you'd be missing some truly great games.
On the other hand, almost every one of those great PS4 exclusives is a 3rd person action game. Yes, they tell moving stories and have great graphics. But the core gameplay mechanics don't really vary that much. The PS4's exclusives are, in all honesty, a bit samey. And most of them are huge, taking dozens of hours to complete. I'm not having a dig at those games, but if you can play TLOU, Uncharted (the whole series; I hadn't owned a PlayStation before), Horizon, God of War & Bloodborne back-to-back, you've got a lot more patience than I have. The Switch has completely distracted me from them over the past few months.
The Xbox has a somewhat better variety of exclusives, ranging from 3rd person action, to FPS, to platformers, strategy games, and racers. They may not be as good, objectively, but there's some real flawed gems among its line-up. Sunset Overdrive, Cuphead, Forza Horizon 2&3, Halo Wars 2, Ori, and Sea of Thieves are some of my favourite games of this generation. Plus, there's Xbox Game Pass and EA Access. Between them, you get access to a huge library of games straight away. You could buy the Xbox on its own and struggle to get bored for months.
Personally, I'd get both (eventually). Which is the best pick now? The PS4 has the standout games that you need to catch up on. The Xbox One is simply better value, once you account for the subscription services. I doubt you'll get bored either way once you throw in some sports titles and the big multi-platform releases.