Heres some info on what sets are used for what encounters
Lesser WardBloodlord Armor Set
Found in: Bastion Stair
Requirements: Ranks: Ranks 37-39
Annihilator Armor Set
Found in: Tier 4 RvR
Requirements: Ranks: Ranks 35-39 and Renown Ranks 31-35
Both sets can be used in any combination to offer the Lesser Ward, which is required for City High Level Dungeons and Fortress encounters. There are five pieces of armor in each set.
Greater WardSentinel Armor Set
Found in: City High Level Dungeons
Requirements: Rank 40
Conqueror Armor Set
Found in: Fortresses
Requirements: Rank 40 and Renown Ranks 45-50
Both sets can be used in any combination to offer the Greater Ward, which is required for both the Lost Vale and the City Invasion PQs. The Sentinel and Conqueror sets also provide the effects of the Lesser Ward. There are six pieces of armor in each set.
Superior WardDarkpromise Armor Set
Found in: Lost Vale
Requirements: Rank 40
Invader Armor Set
Found in: Invasion PQs
Requirements: Rank 40 and Renown Ranks 55-60
Both sets can be used in any combination to offer the Superior Ward, which is required for Sub-Boss PQs. The Darkpromise and Invader sets also provide the effects of the Lesser Ward and Greater Ward. There are six pieces of armor in each set.
Excelsior WardWarlord Armor Set
Found in: Sub-Boss PQs (in cities while contested)
Requirements: Rank 40 and Renown Ranks 64-70
The Sub-Boss PQs are the only means of acquiring the Excelsior Ward which is required for the King Fights. The Excelsior Ward includes the effects of all previous armor sets. There are seven pieces of armor in this set.
Supreme WardSovereign Armor Set
Found in: King Fight (in cities while contested)
Requirements: Rank 40 and Renown Ranks 73-80
The Sovereign armor set is the highest level armor set, and includes the wards from all previous sets. There are eight pieces of armor in this set.
In the source article it mentions a 50% reduction to damage (instead of 200%), this was before the ward change but I believe the rest of the article is correct
Source