I was lucky enough to get my hands on a Copelands trinket, which is awesome. Prior to getting my Copelands i was using 655 Quiescent Runestone and 670 Shard of Nothing, but now i am a bit confused as to which one i should use with the Copelands, seeing as Copeland and SoN shares a 20 sec cooldown.
I am currently using a Copeland's and a HSoN, and I have to say I would be really tempted to use a normal mode Runestone if I had one. I can't speak for the math, but the play style of trying to get the most out of a haste proc that won't ever line up with your typical burst windows feels cumbersome, and I often times find myself just popping SoN randomly just to keep it on cooldown.
My suggestion is to play with both of them for some farm pulls and see how they feel. If you feel like you can get more out of the SoN, go for it, but you might find that the Runestone will serve you better for the time being.