However, some of the questions you raise are not just armor vs all resist but rather mitigation versus life... which is a different story. But if you're purely thinking about those two stats, use the calculator.
What would be better for a Barb who's currently progressing from Grift 46?
Cause I always used Diamonds in my armor and pants, and my Resists were around ±1000. Then I found my Ancient IK 2h and I replaced my Diamonds in my pants with Ruby's.
Then I did another 40'ish (I don't exactly remember) Grift and somehow this went WAY better defensively.
So then I also switched the Diamonds in my armor piece for Ruby's and it went even better.
I also rerolled some %-life stats on my gear pieces to Armor (since I was still around 700-800'ish life) and it just got better and better...
Basically Ruby gems (plain ARMOR gains) went way better defensively as Diamonds did... But can somebody explain me the reason why I should use Diamond gems?
Or even get the all reist stat? What would benefit a Barbarian more? And what would be the ideal range of all resists?
Sorry if this is a noob question, normally I'm not really into Barbarians.