The faster the ram, the better performance from a Ryzen cpu. So while 2133 is base, you'll see @20% performance improvement with 3200. After 3200, prices get ridiculous, so 3200 is as good as it gets value wise.
Right now, because it's so new, Ryzen, unfortunately, is having issues with some high speed ram, mostly SkHynix, which include Corsair, g-skill RipJaws 4 and others. For best compatibility you'll want the Samsung B-die which are found in g-skill Trident-Z and RipJaws V.
Further compatability is found in 2x8Gb sticks, or 2x4Gb sticks, avoid 1x16Gb or 1x8Gb or 4x4Gb.
Rounded out, 2x8Gb g-skill Trident-Z 3200 or RipJaws V is your best bet for best value/performance.
If you just want anything to work, any 2133/2400 is fine, but still a wiser choice to go with 2x sticks in a kit, vrs a single large stick.