The Sampson Awesome set is an end-game set about equal with any of the Celestial Tower ones. Maybe a bit worse, as Sir Sampson the Third has a possibility to appear any time after defeating the 3 Mechanical Bosses, a much earlier feat than the Cultists and their dark lord.
Pieces of the set are not only the armor, but any other drops from the Sir himself. Such as weapons, or pretty much any accessory he drops. Each item as a 12.5% drop rate, but at least ONE is guaranteed to drop.
Helmet of the Acclaimed: Grants 20 Defense, and a 13% Melee damage boost. Looks like the Solar Flare Helm, but dark purple, and without the horns in the back.
Platemail of the Keeper: Grants 26 Defense, and an 8% attack rate boost. Looks like a recolored Hallowed Chestplate when on the player. Also takes on a deep violet color, although slightly brighter, and with a green gem in the middle.
Shinguards of the Divine Warrior: Grants 15 Defense, and a 7% movement speed increase. Takes on the look of Shadow Armor leggings, but again, completely purple, except for the back pixels which are a sickly green.
Armor Set Additional Info:. When all pieces of the armor are equipped, it gives a total of 61 Defense, and as a Set Bonus, every time you get attacked, there is a 40% chance enemies will get paralyzed within 3 tiles. Like a better Brain of Confusion, but doesn't require Expert Mode, and is a lot harder to get.
Greatsword of Crowd Favor: Sir Sampson the Third's page explains more in-depth.
Purple Sovereignty: Also explained more in-depth on Sir Sampson the Third's page. Boosts total Defense from the set up to 69, with the 8 Defense bonus from this shield.
Flail of the Military Leader: Releases two balls that mirror each other, and have a 10% chance to burn enemies. Deals 60-85 damage each.
Chain of the Endurable: It's like the opposite of the Shiny Stone. You heal faster while moving, but since you'll be doing that a lot anyway, it's not nearly as effective as the aforementioned item. About 1/2 of the Shiny Stone's heal rate because of how common your Terrarian moves.
Crown of the Valient: Literally just a Vanity item. Looks pretty regal though. Imagine an average Gold Crown, but with a much larger Ruby in front.
I think this has become the Sir Sampson the Third loot table, rather than just his set. Whatever.
Trophy: Just like any other boss trophy, has a 10% drop rate. Appears to be one of the arm-rests of his throne, held at a diaganol angle. The top laser part emits a faint light when placed.
Mask: HA HA HA! You just became ugly. Sir Sampson the Third isn't the most attractive guy to say the least.
Hallowed Bars: 20-40, because why the hell not?
Chlorophyte Bars: 8-12 also. You need to have beaten the three Mechanical Bosses anyway. Should have a Drax, or Pickaxe Axe by now.
Treasure Bag- Scepter of the Regal Mind (Expert Mode only): The Scepter is a unique weapon that creates a cursed area where you click with it equipped. Has an internal cooldown of 10 seconds. The cursed zone itself lasts 5 seconds, and deals 30-50 damage per second to every enemy standing inside its radius equal to that of the stupid yellow circle that the Lunatic Cultist makes with his ugly decoys. The cursed zone may also inflict a variety of debuffs on targets within it. These include: Poisoned, Cursed Inferno, Confused, and Armor Broken.