AMD are already providing Intel with serious competition with the Ryzen CPUs, both first and second generation, third is going to get interesting.
I bought a Ryzen motherboard bundle, Ryzen 5 1600 / Asus Prime B350 Plus which was heavily reduced in a closing down sale (75% off) just to see what they were like, It actually out performs my i7 6700K on multicore Benchmarks and is pretty close on single core which was a surprise, coupled with the GTX980TI (from Main PC upgraded to 1080TI) It is not far off the i7 / 1080TI performance in TANE / TRS19.
Motherboards? I tend to stick to mid range Asus boards however any from Asus, Gigabyte or MSI should be fine as they tend to use higher quality components across the range.
Xeons require a different socket on the motherboard and probably ECC memory, new looking at £500 upwards just for the Motherboard, for an unthreaded 4 core Xenon around £200 new.
An i5 8600K 6 core unthreaded is around the same price. Motherboard around £250 for a top range Asus, depending on where you look.
Note I've never used AMD GPUs with AMD CPUs, Nvidia work well with AMD.