How do I prioritize Main Stat vs Vit at Paragon levels above 400?

At the absolute latest, you begin putting paragon points into Main Stat and/or Vit at Paragon 401, and they have no cap. How do you determine what the optimal distribution of MS vs Vit is for solo and casual group play at arbitrarily high Paragon levels?

(I am not asking for specific build or character advice, nor asking for recommendations for a tool that will calculate it for me. I'm asking for insight into the underlying math that will inform that decision patch after patch.)

Solution 1:

A Rule of thumb for Vitality vs Dex/Str/Int choice :

• In group casually : if you're playing casually and don't aim for pushing GR further : spend points in Vitality until you never die. This vary vastly depending on the class and the build you play and your skill at the game. Since you're in group you don't have to worry that much about DPS.
• In group competitively : If you're aiming for the highest GR possible, It depends on what role you are playing on the team. If you're support/ZDPS then Vitality first is the way to go, you have to stay alive, not dish damage. On the contrary if you are the DPS then all point go to Main Stat. The ZDPS of the group should take all the aggro anyway so you don't have to worry about dying.
• In Solo casually : Same rule as for casual group except that if you die too frequently, you might want to lower the difficulty level. Farming fatster is more efficient than farming at higher difficulty. I'd go with vitality first until nothing can one-shot you (again it depends on your class/build/skill) then Main Stat.
• In solo competitively : Main Stat first is the way to go if you aim for the highest GR possible. You can't afford to lack damage. Killing faster > Surviving Longer.

This is the order in which I'd prioritize all the Core Paragon point :

1. Movespeed : The movespeed bonus you get from Parangon point + items is capped at 25% . Putting your point in movespeed first will free an affix on your boots to get something like +15% to skill damage. Usually you want boots with Main Stat/ Vitality/All Resistances/Skill Damage. Also movespeed helps a lot staying alive in Greater Rifts.

2. From this point it depends :

• If your build requires you to empty your resource pool in order to deal damage, then maxing max resource is the way to go. Furthemore maxing max resource allows you to take better advantage of items such as Reaper's Wraps which refill your resource based on a percentage of your max resource pool.
• If you don't have to worry about your resource pool and if you are playing a ZDPS (Zero DPS) build, which consist only in you tanking damage and drawing aggro, then you should pick vitality first.
• In any other situation I'd go with main stat. Strength and Dexterity will boost your armor and Intelligence will get you all resistances so no matter what you still get toughness along with a better DPS. When you'll need to push higher Greater Rifts maxing your main stat is mandatory anyway so you don't lack DPS.

However keep in mind that this is a competitive approach of Paragon usage. If you are playing more casually, you might want to aim for vitality first so you don't worry about taking damage and dying until you're comfortable enough to go for more damage.

Solution 2:

There is no hard and fast rule here, in general if you feel that you're dying frequently then you have no choice but add vitality until you are able to make up for it on gear unless you subscribe to the thought that the best defense is a good offense.

Several builds suffer from this problem, demon hunters for example in top end gear feel "squishy". On the other hand even at greater rift 55 a well but not top end geared monk can survive quite well. The demon hunter might add vitality where the monk does not.

Additionally, if you've prioritized life % on gear over vitality then an investment in vitality may quickly pay rich dividends.

How much is vitality worth? At level 70, 100 life per point. source

Straight hit point numbers don't tell the whole story however. 1,000,000 hit points won't last long if you have 0 resistances thus people usually talk in effective health pool.

Effective Health Pool is calculated as TotalHealthPool / (1-Armor Reduction)(1-Resist Reduction)(1-DodgeReduction)*(1-Any other dmg reduction you want). The particular values are explained elsewhere.EHP

The bottom line is, if you don't need the vitality for a particular reason, default to main stat.