Offense Enchantment

Deciding factor: Item Level and Stats

The Offense Enchantments are used to raise the Item Level and change the stat distribution into a more offensive way. There are 4 Defense Enchantment slots available. 2 different three-stat Enchantments , 10 two-stat Enchantments and 5 different one-stat Enchantments exist with ranks from Uncommon (Rank 1) to Celestial (Rank 6). Each upgrade provides 300 Item Level, 270 Combined Rating and 450 stats. Two-stat Celestial Enchantments give 270 more stats due to devs wanting to provide an incentive to get them. Three-stat Celestial Enchantments even give 540 more stats, which makes them the default starting point for any build. Only Celestial Enchantments are shown here. Lower ranks can be taken as starter Enchantments.

For defensive / supportive oriented tanks (Power and CA not capped) the Moonstone, the Bloodstone, the Amethyst Enchantment, the Garnet Enchantment and the Ammolite Enchantment are the most interesting Enchantments. When you have no Celestial Enchantments yet:

Two-stat Enchantments are good when you play only one toon and want to min-max.
The Ammolite Enchantment is good when you started with them, but do not require them in defensive slots anymore!
When you play multiple toons, then the Garnet is interesting as it provides also great Defense boosts for defense slots on damage dealers and healers.

One - Stat Enchantments, Two - Stat Enchantments, Three - Stat Enchantments. What is the offensive BiS for Tanks?

Well this question might be raised, while reading this and the answer is not straight forward like for the main defensive stats, where Three - Stat Enchantments have a higher value than Two - Stat Enchantments and where Two - Stat Enchantments have a higher value than One - Stat Enchantments. Because tanks lack on all 5 offensive stats ratings and percentages, Critical Strike, Critical Severity and Accuracy are typically on the low side and have little value for tanks. Thus the Two - Stat Enchantments with Power and Combat Advantage are still better than Three - Stat Enchantments that provide more stats! For tanks, Three - Stat Enchantments are closely as valuable as One - Stat Enchantments!

This is similar to damage dealers and healers, when they thinking about what they should slot in their defensive slots!