Depending on your choice in the Blacksmith Quest, you will either have Angrim or Duncan.

Angrim's Bonuses:

• 3-7% Pierce Resistance
  
• Increases Armor Protection by 2-4%
  
• +2-4% Physique

Duncan's Bonuses:

• Increases Energy Regeneration by 8-16%
  
• +4-12 Defensive Ability
  
• +2-4% Physique

Angrim is always a solid choice to choose, as early on when you will be using them, extra armor or rare (at that point in the game) pierce resistance is a much better choice than extra energy regen or DA. Late and end-game however, Duncan offers convenient access to his bonuses that are better for some caster characters (the energy regen and potential bonus DA). However, other smiths in the game offer access to that same energy regen bonus. Although, if the resistances that those other smiths offer would be capped or are capped on your character (bleeding & vitality), then Duncan offers you a chance between the always useful DA, energy regen, or percentile increase to Physique.

Generally, you should pick Angrim on Normal, Duncan on Elite, and who ever is better for your character on Ultimate.

One last thing is that they offer 4 different low level (15ish) items that only they can craft. Angrim offers warrior type weapons, while Duncan offers caster type weapons.

These blacksmith are available at Homestead & Fort Ikon. They offer the same bonuses, which one you choose is purely a matter of convenience, although Fort Ikon's smith is closer to the Smuggler.

• 2-4% Aether Resistance
  
• 2-4% Chaos Resistance
  
• +38-80 Health

These smiths are useful in the mid-point of the game on your character's first play-through, but the health bonus is just pure sh.‏‏‎it even at that stage in the game. Late and end-game, the bonus to aether or chaos resist is often not necessary, as the gear or devotions you have at that point in the game will often cap those resists. Rolling the garbage health bonus at that point will make you want to shoot yourself even more too.

Their one saving grace is that they can craft Dynamite.

These smiths are either in the Necropolis, or more conveniently, in the Crucible. They offer the same bonuses, meaning that if you just want to craft something, fire up the Crucible.

• Increases Energy Regeneration by 8-16%
  
• 3-7% Bleeding Resistance
  
• 3-5% Vitality Resistance

These bonuses are solidly mid-tier. In the mid-game on normal/elite they can be helpful. But in the end-game Bleed and Vitality resist will often be capped or overcapped by your gear or devotions. If these resistances were less common they'd be more valuable, but they are not.

The Necropolis Smith can exchange vanilla materials for another, plus a cost of 5,000 iron.

• Ancient Heart >>> Blood of Ch'thon
  
• Blood >>> Tainted Brain Matter
  
• TBM >>> AH

Lastly, the Crucible Smiths can craft Dynamite.

Necropolis Smith location:

These next 2 smiths are both really good, their bonuses are universally useful, and are part of my holy trinity of good smiths. I will go into detail on the bonuses in the final section.

Kaylon - Forgemaster: Found in Malmouth Steelcap district after you unlock him as part of the story.

• 2-6% Reduced Stun Duration
  
• 2-6% Reduced Freeze Duration
  
• +2 to +6% Shield Damage Blocked

Gaius Ember - Burning Smith: Found in the Malmouth Outskirts, see the end of this section for map location.

• 2-4% Poison & Acid Resistance
  
• Increases Energy Regeneration by 8-16%
  
• +1-3% Crit Damage

Kaylon can craft Dynamite and exchanges vanilla crafting materials for AoM crafting materials at a cost of 35,000 iron, this is a one-way transfer so be mindful of that.

• 6 Tainted Brain Matters >>> Aetherial Missive
  
• 6 TBM >>> Aetherial Mutagen
  
• 6 Ancient Hearts >>> Wendigo Spirit

Gaius can exchange the AoM crafting materials for one another plus 10,000 iron.

• Wendigo >>> Mutagen
  
• Mutagen >>> Missive
  
• Missive >>> Wendigo

Gaius' Location:

The FG smiths are a hit and a miss. The first available FG smith, Ignus - Bewitched Smith, is absolute trash, with his only benefit being convenience and the ability to craft dynamite.

Ignus - Bewitched Smith:

• +8-12% to All Retaliation Damage
  
• +38-80 Health
  
• Healing Effects increased by 2% - 4%

These bonuses are pure garbage. Retaliation builds are purely meme jank. The health bonus is as worthless here as it was on the Legion smiths. Lastly, the healing effect bonus is too small to be of any value, even if you crafted what you could for your set (Helm, weapon, neck, medal) and got the max god roll of 4% increase, you would only have 16% increase in your healing effects, which almost all overheal you anyway, and which you could have replaced those 4 bonuses with something better from one of the holy trinity smiths. The final nail in this mechanic's coffin is that "Healing Effects increased by %" do not increase your passive health regeneration at all.


The next smith is the final member of my holy trinity of good smiths, a shame that he is not located too conveniently.

Egellon - Forgotten Smith: Found in the Sunbane Oasis, see end of this section for map location.

• +4-12% Slow Resistance
  
• +1-3% Movement Speed
  
• +2-6% Reflected Damage Reduction

I will go into detail on these bonuses in the final section.
Egellon can trade 1 Celestial Lotus plus 10,000 iron for 1 Eldritch Essence. A bad trade considering the commonality of EE, but an option nonetheless.
Egellon can also trade 1 Celestial Essence plus 5,000 iron for a random crafting material (TBM, Blood, EE, Mutagens, ect.).

These rare FG crafting material exchanges can be done at ANY smith. They are:

• 35,000 iron + 1 polished emerald + 25 Ugdenbloom >>> 1 Celestial Lotus
  
• 25,000 iron + 4 EE >>> 1 Celestial Lotus
  
• 35,000 iron + 1 polished emerald + 10 Aetherial Mutagen >>> 1 EE

Egellon's location:

The Celestial smiths all offer the same bonuses, however, they can only craft random legendaries.

• Increases Health Regeneration by 5-11%
  
• +4-12 Defensive Ability
  
• +4-12 Offensive Ability

They only appear on elite and ultimate difficulty in Tyrant's Hold, the Tomb of Herald Mathis (AoM), and the Tomb of Nephos (FG).

The Tyrant's Hold Celestial smith can only craft legendaries up to level 75. The DLC Celestial smiths have no level restriction.

The costs vary:

• Vanilla takes 8 of one rare vanilla material (Blood for Armor, TBM for Weapons, AH for Accessories & Ranged) plus 75,000 iron and 1 polished emerald.
  
• AoM takes 6 of one AoM rare material (Missives for Melee and armor, Mutagens for Caster weapons and Ranged, Wendigos for Accessories) plus 125,000 iron and 1 polished emerald.
  
• FG takes either 4 Eldritch Essence for Armor & Accessories or 2 Celestial Lotuses for Weapons plus 125,000 iron and 1 polished emerald.

You must be level 50 to craft legendaries (58 for accessories), otherwise you get an epic. It's better to wait till you either hit 65 (for vanilla) or 94 (for the DLC smiths).

Kaylon - Forgemaster: Malmouth Steelcap District:

• 2-6% Reduced Stun Duration
  
• 2-6% Reduced Freeze Duration
  
• +2 to +6% Shield Damage Blocked

The weakest of the three, Kaylon offers useful crowd control reduction stats and a nice bonus for shield tanks.
Stun resist is universally useful, but can sometimes be easily capped depending on your character, for those who can't easily cap it, this bonus is ideal.
Freeze resist is less universally useful, with the enemies who inflict freeze being quite rare (note that the Undead Nemesis and Steps of Torment final boss are much easier with freeze and cold resist), and also the easy availability of Hoarfrost Ointment, still a decent bonus if only due to scarcity.
The Shield Damage Blocked bonus is ideal for tanks who are capped on whatever other resistances they already have.


Gaius Ember - Burning Smith: Malmouth Outskirts:

• 2-4% Poison & Acid Resistance
  
• Increases Energy Regeneration by 8-16%
  
• +1-3% Crit Damage

The lottery machine of the three, Gaius offers 2 bonuses that can be found elsewhere, but offers a final bonus that is rarely found on gear and is universally great.
Poison resist is fairly common, with some builds being overcapped by their skills (occultist), gear, or devotion. However, Poison resist can be somewhat hard to find for soldier types, so getting this bonus might just free up an augment slot for one of the nice FG faction augments like Dreeg's Omen.
Energy regen is a bit of a miss at this stage of the game, you should be drowning in elixirs of spirit, if not already having enough energy regen from your devotions or gear, but this could still prop you up if necessary.
The crit damage bonus is the jackpot. Literally every build benefits from this stat. GET IT.


Egellon - Forgotten Smith: Sunbane Oasis:

• +4-12% Slow Resistance
  
• +1-3% Movement Speed
  
• +2-6% Reflected Damage Reduction

The reliable of the three, Egellon offers universally useful and hard to find bonuses that no other smith offers.
Slow resistance is great for all builds, but especially useful for melee builds relying on WPS attacks or caster builds that spam something.
Movement speed can be capped easily depending on your devotions and boot augment, but this bonus might just let you put a different boot augment on if you get it.
Reflection Reduction is very useful, but is absolutely necessary for any physical build that deals internal trauma damage. With this bonus combined with the relevant devotions, you just might not die from your own internal trauma dot because you accidentally forcewaved a Skeleton Knight.


Hope this guide helped!