First of all a list what stat bonus does what.
HP UP = +50 HP
Defense Up = +2 Defense
Attack UP = +2 Attack
Magic UP = +2 Magic
Attack Rating UP = +50 Attack Rate
Defense Rate UP = +20 Defense Rate
Critical Damage UP = +10% Crit DMG inc.
Not every item can get every stat bonus lets start with a list of all catalysts and what they do.
Ah 2h Sword gets doubled stats because it replaces 2 Items (thx 4 information guide readers)
Helm = HP UP
Suits = Defense UP
Gloves = Attack Rate UP
Shoes = Defense Rate UP
Orbs/Crystals = Magic UP
1h Weapons = Attack UP
2h Weapons = Crit DMG inc.
but for example a two hand sword cant get +HP. so i also got a list wich shows wich kind of item can get wich stat bonus.
Helmets = Defense, Defense Rate, Crit DMG
Suits = HP UP, Defense, Defense Rate
Gloves = Defense, Attack Rate, Defense Rate, Attack
Shoes = HP UP, Defense, Defense Rate
1h Swords = Attack Rate, Attack, Crit DMG, Magic
2h Swords = Attack Rate, Attack, Crit DMG, Magic
Orbs/Crystals = Attack Rate, Attack, Crit DMG, Magic
For expample you got a slotted bluestin helm and you want to upgrade it.
You can choose between Defense, Defense Rate and Crit DMG.
So you maybe think: ah, iam a blader and got high crit rate i want more crit dmg.
Then you have to use a 2h sword with the quality of slotted Bluestin or higher.
This how-to should help you to choose the right upgrades for your armor without testing everything.