I assume preference is in that order? My goal to keep over 600hp and 1100+ res
It’s for the chest. All are great. Problem is - if you can roll 130 AR on it, it has not secondary resist - so I’d take Allresist. Some might say Elite DR (it’s very rare and hard to roll) but not all elite attacks are covered by elite DR and impossible to say. Most fierce attacks are physical, allresist is always good, but if you have an item that has no allres it should always have a secondary resist roll (like your helmet for instance). Ideally physical, followed by fire. But there should be something on it.
+15 life is great for ballista/Squirts when you can’t have AR. So ideally a chest with 210 phys resistance - but you don’t want to have no resist at all on a chest and go for +life
+life vs vit: Vit is better, but with enough paragon you can buy vitality via paragon points. There is some point where +life beats vitality because of that.
TLDR: Allresist in this case. If there would be a secondary resist on the chest, I’d take elite dr.
I’m not sure what the formula is because I’m terrible at math but I’d say with Ballista the closer you can get to a total of Life + Ballista Shield to equal 1 mil the better. I ran with 11% Elite DR on my chest for the longest time but when I switched to Life % (the chest had a single resist secondary, Arcane I believe), the shield had more hit points, I had more hit points and taking a hit from non elites (which are the vast majority of mobs you’ll find in a Grift) was less likely to kill making it easier to avoid dangerous elite affixes.
Completely anecdotal I know but that’s my experience anyway.
It doesn’t really matter. Anything that increases your regular toughness also increases your shields (or at least, shields that scale as a % of your HP, anyway) by an equivalent amount. There’s no difference in your shield value between having 1m HP and less damage reduction vs. having 750k HP and more damage reduction. If your total toughness is the same in both scenarios, your shield strength is also the same.
Generally speaking, elite reduction will give you a bit more toughness vs. elites compared to 15% life, but a lot less toughness vs. non-elites.
There’s a few cases where you might prefer mitigation stats like elite reduction over % life, but that’s generally for situations where you are relying on flat healing (e.g. life per hit) and aren’t getting one-shot. The idea is that with mitigation stats, each point of health healed by your life per hit is worth more overall toughness so you’re effectively healing more toughness over time. But with life% and life per hit, you aren’t healing any more toughness over time, it just takes longer to recover fully. With flat healing, life% increases your total toughness but not your toughness recovery over time, but mitigation stats increase both your total toughness and your toughness recovery over time.
With shields that are based on a % of your max HP (e.g. Fortress Ballista and wizard shields, but not Molten Wildebeest’s Gizzard) it’s a bit different. Increasing your % life both increases your shield recovery rate and your total shield size.
So basically with Fortress Ballista it doesn’t matter. Whatever maximizes your regular toughness also maximizes the value of your shields.
EDIT: I should add I also prefer life % over elite reduction. I think people get a bit fixated on elite reduction because it’s a rare stat, and they assume rare = better. But elite reduction is pretty situational. Life% is slightly worse vs. elites but gives you better balance overall.