It really depends on your build and your playstyle…

I personally play full Agility and I dodge most thing so I don’t need high armor.
→ Ranger Armorset (unlocked via Dungeon Delver Journey) + Silent Legion Medium Pauldron for a bit more protection.
↳ With a T4, this give me a total of 392 Armor = 43% dmg reduction, but the important part is +40% Agility Weapon Damage and +28 Stamina.

If you’re playing Authority (+Agility), you pick the Master Skelos Cultist Armorset because it gives you a ton of follower damage.

If you prefer playing Strength Weapons, you have plenty of choices depending on whether you want light medium or heavy armor, but for maxium damage you pick Redeemed Legion Helmet, Voidforged Dragon Ribs (you have other options that aren’t heavy here), Silent Legion Medium Gauntlets, and then any pieces that give you +5% Strength (with a T4) on Pants and Boots.

Of course I’m only talking about Exiled Lands, because on Siptah you get a few more options like the Black Knight Tasset giving +8% Strength with T4, while on Exiled Lands you can only get +5% afaik.