Okay these are I guess typical newbie questions, but I do not want to regret my choices later because I got rid of something that was better then the other in some way?
Which of these would more experienced GD players use with a level 20 character. ( Well … use until something clearly better comes up that is. )
Chest: https://imgur.com/Tca8Zek
Boots: https://imgur.com/uNaz7sa
Shoulders: https://imgur.com/BkBoDs2
Imho. 
The only one where I would hesitate would be the shoulder piece
At low level I would opt for the stat boost instead of the flat HP unless you did move your Mastery very high already those extra 5-10 points in each stat will help you more than the 75 flat HP and Shaman already offer a lot of HP anyway.
Green Chest
Blue Boots
Thank you very much Rhylthar and Krawl, in that case I will take these already …
1: Green
2: Blue
@krawl
As for the Mastery bar … well it is currently this?
I am following this build …
I would prefer Isaac. And don´t worry, I think you will get another (better) shoulders in about 2 - 4 levels. 
Hmm now I am getting very curious, now I have to play again this evening. 
And for now I did stay with Isaac, I just changed the other two.
Go with Isaac 32 at level 20 is kinda high but not Very high (some build will rush to 50 to get one specific skill for exemple) the set of stats will be more usefull to you than the HP.
Also at your level gear will change “fast”
Yeah I started to notice that already.