Best is relative. Motherboard choice is a balance of hardware features, power delivery, and bios options. All of these things really have little to do with chipset and more to do the individual board. There are a ton of crap x370/x470 boards. I've owned about 30 AM4 boards and have done a ton of research on this subject. There are in reality only a handful of really high quality 300 and 400 series boards at least in terms of power delivery. The tomahawk is often recommended because it has good power delivery for the money. In terms of features it's not that great. I personally think it's overrated. Power delivery info for AM4 is available here:
Power delivery really isn't as big of a concern for the 6 and 8 core 3000 CPU's. They just don't draw enough current or have enough OC headroom for power delivery to be a big concern. As long as it has reasonable power delivery and the features you want (readily available on the product pages) then you are good to go. In general the better the board the more advanced bios options you will have. If you aren't going to tweak your settings to squeeze every ounce of performance out of your system then this probably doesn't really matter either.
Since you are running 4k the CPU won't be much of a factor anyway. You'll be completely GPU bound at 4K with any currently available GPU. I'd recommend the 2700x since they are blowing them out for dirt cheap . I bought 2 of them for $130 a piece in November.
That was my initial choice ! But then I have seen some tests and 2700x has a lot of frame drops and stuttering in games. Also worse single-thread performance.
But it's half the price of 3700x, which means, I could use the money for a better GPU !
Anyone having issues with stuttering or dropped frames of 2700x ?
It would for sure be the best bang for buck now ! 😱😍