Good question.
In fact BiS is hard to determine, instead of a BiS set in the stone that will be modified each time a new piece of equipment becomes available, I'd like to use the following priority list to determine which equipment should be used in each slot:
1) First meet your [Accuracy] quota
What a lot of people does not know about accuracy is that given the directional nature of the game combat mechanics, the accuracy required to hit an enemy from the front, from the side and from the back is different. For example in order to hit Twintania in BC Turn 5 you need: 481 from the front, 473~ from the side and 440~ from the back.
Therefore usually tanks require the highest accuracy followed by the melee DPS's and finally the ranged DPS's, it does without saying but healers do not require accuracy for recovering spells.
As far as I understand there is no accuracy requirement for anything outside Bahamut Coil, hence you can have one set for BC and other set for everything else.
2) Tanks, mind your [Defensive Stats]
Every defensive accessory in this game has VIT so there isn't much of a choice there. What you need however is Parry, there isn't much else to consider as far a defensive stats are concerned.
As a Tank you should be concerned only with your Weapon damage above parry, any other offensive stat should come second to your survivability.
3) Finally focus on your [Offensive/Healing stats]
Weapon damage: 49
Main Stat: (STR, DEX, INT, MND): 6
Determination: 2
Critic Damage and Spell/Skill Speed: 1
Note: again this values are approximate but close enough to the real thing to be used for comparisons.
It's also worth mention that while critical chance and spell/skill speed have more or less the same weight the former is a free damage/healing increase, while skill/spell speed increase your resource (MP/TP) consumption which is not really desirable.
[Exceptions]
- Bards and Scholars have mechanics that greatly favor critic chance, hence for them the weight for Critic chance is about 3~ I haven't check this number myself but most people seem to agree on it.
Another thing to mention is that given the weight of each stat it's extremely rare that a lower ilvl piece outperforms a higher ilvl piece given the higher ilvl will have at least 2-3 points difference in the main stat.
I'm sorry the post got a bit long, but I hope it helps.
Ken
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"Maybe it means: you're the evil man, and I'm the righteous man, and Mr. Nine-millimeter here, he's the shepherd protecting my righteous *** in the Valley of Darkness." - Jules.
FFXIV: Mabel Rand (Gugnir) FFXI: Kenage, retired. K&K forever!,