I was in the exact same situation, trying to decide between a B450 or X570 board.
I purchased a Ryzen 3700x and have no real need for pci-e 4.0 right now but I wanted to future proof more than what the B450 chipset would allow me.
So....
I decided on this board:
MPG X570 GAMING PLUS
It's a "gaming" board and even tho it has headers for RGB lighting it actually has no RGB lights on the board.
My criteria was :
X570 chipset
Price
Excellent rating.
That board is the cheapest x570 board with a 5 star rating on Newegg.
There was one issue I was worried about, lots of talk of X570 boards being loud because of the chipset fan but this boards chipset fan only runs when needed.
I just looked and as of this moment it is not running at all.
I have had ZERO issues.
Setup:
MSI motherboard listed above.
3700x cpu
Samsung 500 gb SSD for windows
240 Intel SSD for Ubuntu 18.04.2
32 Gb of Gskill Trident Z 3200 ram.
PowerColor Red Devil RX580 video card
Stock AMD cpu cooler
Added a PCI-e USB 3.0 card for more usb connections, had it laying around unused.
Phantek Entho Pro case, this is the 5th motherboard I have had in it. Great case!!
I am REALLY impressed with the onboard sound quality, noticeably better than even a couple of nice PCI-e sound cards I have.
The board is flat black with a few red highlights but is really understated and looks nicer than the "server green" asrock rack dual xeon board that I took out.
So far super impressed with the performance, I can even game at 4k with the Rx580.
Just about the only gaming I do is World Of Tanks, and have a older pc that plays it really nicely with a 1080p monitor that I was planning on using to keep gaming on but I installed Windows 10 and then WOT just to try it out.
I was really planning on this being a Ubuntu only box but WOT looks AMAZING at 4k I decided to buy a Windows 10 key and keep windows 10 on it and dual boot with Ubuntu.
I was not really expecting it to game at 4k but it plays WOT REAL nice at 4k with everything set on ultra, I average ~35-~42 ish frames per second and butter smooth.
Have no regrets at all, its the first MSI board that I have purchased and I highly recommend it.