Magic Damage or Intelligence

[Altena]

Ignore iLvl for now.. Go on a priority system..

Weapon Damage > Main stat (STR,VIT,INT etc) > Accuracy > Substats

Weapon damage is king.

Then go for your "main stat". Your main stat increases damage, but each main stat has a sub effect (such as VIT gives you more HP)
VIT > Tank
STR > DRG/MNK
DEX > NIN/BRD/MCH
INT > SMN/BLM/ACN (Throwing this in here for levelling purposes)
MND > Healer

Accuracy only until you stop missing. Excess accuracy does nothing for you. For the sake of leveling purposes you should be fine with whatever you decide to equip. This comes more into play later on when you get to level cap etc.

Substats.. This varies again depending on your job, and how it plays..
For example, generally a melee DPS will prioritize Crit & Det, whereas a BLM may prefer Crit & Spell Speed..

Crit - Increases critical hit rate (both weaponskill & auto attack)
Det - Increases damage per hit (weaponskill & auto attack)
Skill/Spell Speed - Reduces GCD cooldown & increases DoT tick damage.
Parry - Ignore this trashy substat. It's by far the most useless (at the moment).

When it comes to "defense" for tank gear, generally anything that can only be worn by a tank (GLD PLD MRD WAR DRK) is designed for a tank.
If the gear has any other melee class on there (such as LNC / DRG) it is more of a DPS piece.
Generally speaking while you level, you can get away with the hybrid style body pieces that both a tank & DPS can wear, however keep the priority system in mind - choose what to wear based on the main stat (VIT for a tank).

I say this, mostly because damage matters when you're a tank and you're leveling, even moreso than defense in my opinion. Mostly because when you enter a new dungeon to level up, you are at the lowest level you can enter it most of the time. Quite often the DPS in your party are higher level then you, and probably overgeared, so keeping hate is a bit more challenging if you don't have the damage to do it.

Hope this helped.