For accessories: Either, just not neither.

For armor: Defense and Magic Defense over both (these account for more mitigation than either STR of VIT will provide, which will make you less squishy).

For weapons: Weapon damage.

For shields*: Kite > Scutum > Hoplon
*in my experience

For sockets: Don't bother.

Rotate your cooldowns, rotate targets for enmity combo, and stay in your tank "stance" and you'll do fine.