It is not an easy question to answer as items frequently offer multiple boosts. How do you compare an item offering 30% Troop Attack with one offering 20% Troop Health + 20% Defense Debuff?
Hopefully this list will help solve the problem. It adds together all the combat boosts to find the items that offer the highest total combined boost.
These boosts include: Attack, Defense, Health and Defense Debuff.
There are two lists: attacking items and defensive items.
Check it out here: