Ryzen 7 3700x is more than enough for most people. Ryzen 9 3900x is major overkill.
Since we're talking about me I would get the Ryzen 7 3700x because it is a better deal than the 3800x and the Ryzen 9 is way out of my usual budget. I usually try to save as much as possible for a better graphics card. If I already had the best GPU though I would definitely get the 3900x because it is better than anything Intel offers on mainstream. Intel can't compete unless they lower prices or do something dirty like they've done before when AMD was ahead in the past. I like intel but I wouldn't get a 9900KS unless it was heavily discounted because 1. It's a dead platform 2. It's 8 good cores vs 12 good cores. Obviously I wouldn't go for 8 cores when I could get 12. In the bulldozer days AMD had twice the core count and Intel still won. Those days are over for now. I'd be willing to bet that soon Intel will leap ahead again and AMD will try to fight back with higher core counts and lower prices but I don't know when it will happen.
Ill just leave this here 36 game test if you don't feel like reading video. You can also watch this where they talk about AMD vs Intel youtube and why someone might choose one over the other.
but for me
straight gaming -> intel
gaming plus streaming -> i would look hard at AMD
any multi core activities -> AMD
Questions: causal graphic design/video editing, and for occasional general day to day administration and report generating work. Are you getting paid for any of this? Do you care how long it takes to finish these tasks?
If you answer no to both of these go intel. If ether of the answers is a yes look at AMD.