Str and Vit provide equal damage bonus for tanks. Vit is better because it provides health and damage, but it can't be melded to tank accessories. Str can be melded and is a main stat for tanks, which means it is the best choice for melding accessories. Other classes would be ecstatic to meld more main stat. Don't give up this big advantage by melding something else.

If you think parry or speed or anything else is better, just trust the forums on this and go Str. You'll do more damage and hold aggro easier as people gear up with lore. You can't meld Str to armor, so put whatever secondaries you like on armor. Crit and Det are the best choices (more damage and easier aggro), but there is more flexibility because they are just secondary stats. Put speed or parry there.