Best Render Engine, HDRI's for Rhino In 2019 For Diamond Jewelry

Too much light in your render comes from HDR map not the engine itself. try different maps for refraction, rotate them play with them.

Jewellery rendering has been on here many many times already just do a bit of digging :wink:
No point of looking for “best engine of 2018,2019 and so on” All (most) engines can give you pretty much the same output it’s only the difference in the way you’re getting to the result.

I personally use Thea render these days…used to use Vray, Arion, Maxwell, Keyshot and few others.

Some examples here

PS. Don’t ignore importance of your light setup and hands down tool to go is HDRLightStudio