Best in slot (BiS) items often depends on the boss you are up against. As a result it might be a good idea to keep different gear at hand for certain bosses. The list below contains the BiS items for protection warriors in PvE, through the different content releases in WoW Classic. Not all items may be perfect for your build, but it should serve as a reference.

Phase 1 Pre-Raid

Slot Item
Head Gyth's Skull / Mask of the Unforgiven
Neck Medallion of Grand Marshal Morris
Shoulder Stockade Pauldrons
Back Stoneskin Gargoyle Cape
Chest Deathbone Chestplate / Savage Gladiator Chain
Wrist Runed Golem Shackles / Battleborn Armbraces
Hands Stonegrip Gauntlets
Waist Deathbone Gridle
Legs Legplates of the Eternal Guardian / Cloudkeeper Legplates
Feet Deathbone Sabatons / Sapphiron's Scale Boots
Ring Naglering / Painweaver Band
Ring Drakeclaw Band of the Monkey / Blackstone Ring
Trinket Force of Will / Blackhand's Breadth
Trinket Demon's Blood / Hand of Justice
Main-Hand Mirah's Song / Ironfoe / Axe of the Deep Woods
Off-Hand Draconian Deflector
Ranged Blackcrow

Phase 2 Pre-Raid

Slot Item
Head Gyth's Skull / Lionheart Helm
Neck Medallion of Grand Marshal Morris
Shoulder Stockade Pauldrons
Back Redoubt Cloak
Chest Deathbone Chestplate / Savage Gladiator Chain
Wrist Fel Hardened Bracers / Battleborn Armbraces
Hands Stonegrip Gauntlets
Waist Deathbone Gridle
Legs Legplates of the Eternal Guardian / Cloudkeeper Legplates
Feet Deathbone Sabatons / Sapphiron's Scale Boots
Ring Naglering / Tarnished Elven Ring
Ring Drakeclaw Band of the Monkey / Blackstone Ring
Trinket Force of Will / Blackhand's Breadth
Trinket Demon's Blood / Hand of Justice
Main-Hand Mirah's Song / Ironfoe / Axe of the Deep Woods
Off-Hand Draconian Deflector
Ranged Satyr's Bow

Phase 2

Slot Item
Head Helm of Wrath / Lionheart Helm
Neck Medallion of Grand Marshal Morris
Shoulder Pauldrons of Might / Stockade Pauldrons
Back Redoubt Cloak
Chest Deathbone Chestplate / Savage Gladiator Chain
Wrist Bracers of Might / Wristguards of True Flight
Hands Stonegrip Gauntlets / Gauntlets of Might
Waist Belt of Might / Onslaught Girdle
Legs Legplates of Wrath
Feet Sabatons of Might
Ring Naglering / Band of Accuria
Ring Heavy Dark Iron Ring / Quick Strike Ring
Trinket Force of Will / Blackhand's Breadth
Trinket Onyxia Blood Talisman / Hand of Justice
Main-Hand Eskhandar's Right Claw / Quel'Serrar / Ironfoe / Deathbringer
Thunderfury, Blessed Blade of the Windseeker
Off-Hand Drillborer Disk
Ranged Satyr's Bow / Striker's Mark

Phase 3

Slot Item
Head Helm of Wrath / Lionheart Helm
Neck Master Dragonslayer's Medallion
Shoulder Pauldrons of Wrath / Stockade Pauldrons
Back Redoubt Cloak
Chest Breastplate of Wrath / Savage Gladiator Chain
Wrist Bracelets of Wrath / Wristguards of True Flight
Hands Gauntlets of Wrath / Gauntlets of Might
Waist Waistband of Wrath / Onslaught Girdle
Legs Legplates of Wrath
Feet Sabatons of Wrath / Chromatic Boots
Ring Naglering / Band of Accuria
Ring Heavy Dark Iron Ring / Quick Strike Ring
Trinket Styleen's Impeding Scarab / Drake Fang Talisman
Trinket Onyxia Blood Talisman / Blackhand's Breadth
Main-Hand Spineshatter / Crul'shorukh, Edge of Chaos / Ironfoe / Deathbringer
Thunderfury, Blessed Blade of the Windseeker
Off-Hand Elementium Reinforced Bulwark
Ranged Dragonbreath Hand Cannon / Striker's Mark

Phase 4

Slot Item
Head Helm of Wrath / Lionheart Helm
Neck Master Dragonslayer's Medallion
Shoulder Pauldrons of Wrath / Stockade Pauldrons
Back Overlord's Embrace / Zulian Tigerhide Cloak
Chest Breastplate of Wrath / Savage Gladiator Chain
Wrist Bracelets of Wrath / Wristguards of True Flight
Hands Gauntlets of Wrath / Gauntlets of Might
Waist Waistband of Wrath / Onslaught Girdle
Legs Legplates of Wrath
Feet Sabatons of Wrath / Chromatic Boots
Ring Overlord's Crimson Band / Band of Accuria
Ring Heavy Dark Iron Ring / Quick Strike Ring
Trinket Styleen's Impeding Scarab / Drake Fang Talisman
Trinket Onyxia Blood Talisman / Blackhand's Breadth
Main-Hand Chromatically Tempered Sword / Crul'shorukh, Edge of Chaos / Ironfoe
Thunderfury, Blessed Blade of the Windseeker
Off-Hand Elementium Reinforced Bulwark
Ranged Dragonbreath Hand Cannon / Striker's Mark

Phase 5

Slot Item
Head Helm of Wrath / Lionheart Helm
Neck Mark of C'thun
Shoulder Pauldrons of the Unrelenting / Conqueror's Spaulders
Back Overlord's Embrace / Cloak of Concentrated Hatred
Chest Breastplate of Wrath / Conqueror's Breastplate
Wrist Bracelets of Wrath / Wristguards of True Flight
Hands Gauntlets of Steadfast Determination / Gauntlets of Annihilation
Waist Royal Qiraji Belt / Onslaught Girdle
Legs Legplates of Wrath / Conqueror's Legguards
Feet Sabatons of Wrath / Chromatic Boots
Ring Ring of Emperor Vek'lor / Band of Accuria
Ring Heavy Dark Iron Ring / Don Julio's Band
Trinket Styleen's Impeding Scarab / Drake Fang Talisman
Trinket Onyxia Blood Talisman / Blackhand's Breadth
Main-Hand Ancient Qiraji Ripper / Crul'shorukh, Edge of Chaos / Ironfoe
Thunderfury, Blessed Blade of the Windseeker
Off-Hand Blessed Qiraji Bulwark
Ranged Dragonbreath Hand Cannon / Crossbow of Imminent Doom

Phase 6

Slot Item
Head Dreadnaught Helmet / Conqueror's Crown
Neck Mark of C'thun / https://classicdb.ch/?item=21329
Shoulder Dreadnaught Pauldrons / Conqueror's Spaulders
Back Cryptfiend Silk Cloak / Shroud of Dominion
Chest Dreadnaught Breastplate / Plated Abomination Ribcage
Wrist Dreadnaught Bracers / Wristguards of Vengeance
Hands Dreadnaught Gauntlets / Gauntlets of Annihilation
Waist Dreadnaught Waistguard / Girdle of the Mentor
Legs Dreadnaught Legplates / Conqueror's Legguards
Feet Dreadnaught Sabatons / Chromatic Boots
Ring Ring of the Dreadnaught / Band of Unnatural Forces
Ring Ring of Emperor Vek'lor / Ring of the Qiraji Fury
Trinket Styleen's Impeding Scarab / Kiss of the Spider
Trinket Drake Fang Talisman
Main-Hand The Hungering Cold
Thunderfury, Blessed Blade of the Windseeker
Off-Hand The Face of Death
Ranged Dragonbreath Hand Cannon / Soulstring

Source