For starters, let me say I'm a demon hunter. So i farmed a new pair of reapers wraps and am having a tough time deciding what to re-roll. Keep in mind I'm also a cluster arrow fire build. It came with increased fire dmg, dex, vit, armor, and fire resistance. I want to know whether it's a better idea to reroll crit chance to replace vit or dex. I currently have 298K health and 3.9m toughness.
you will loose a huge ammount of toughness if you replaced vit into cc. However replacing armor with cc won't have much impact on your toughness and it's the only reasonable thing to reroll on the bracers
Just saying this - having a huge HP pool doesn't mean anything if you take full damage from abilities.
Mitigation is basicaly mandatory - you should aim to have 70% dmg reduction from AR and armor before entering high difficulty levels.
This is easily achievable through Awareness - Perfectionist - Boar pet. With 4 mara and a good chunk of AR you don't need Perfectionist, and Awareness just makes sure you don't need to roll Armor as affix.
I tend to avoid %life if you have enough VIT - true is that not alwaysyou gear is perfect so %lif is a really good placeholder to get you around 400/450k hp which is plenty to go in any difficulty (and i play conservative, people play with much less sometimes).
Mitigation and life regen are what matter most. You need to reduce the incoming damage as much as possible and match it with life regen. Mitigation makes life regen more efficient, so you need fewer items with life regen. Vitality simply increases how much burst damage you can sustain without dying. But It doesn't (normally) help you get your life back. It's for surviving stuns, freezes, and big hits. Those should be rare situations where you can easily recover your life with a potion.
It's hard for anyone to tell you what you need more without a thorough investigation of your character and what difficulty you're playing. But you should be able to play, see how low your life dips when frozen or hit hard, and judge from that.
I would also like to add that I've found resist all to be better than armor for pretty much every class, even for int users, and even when using passives to boost armor by a percentage. I know it doesn't help the OP in his current situation, but it's useful to keep in mind for future upgrades.