CHA stacking Oathbreaker Paladin (7) / Hexblade Warlock (5)

https://www.dndbeyond.com/forums/dungeons-dragons-discussion/rules-game-mechanics/107685-very-important-question-the-ultimate-smiter-cleric

What gets tricky about this design (stacking a bunch of CHA modifier damage on our weapon) is that multiclassing Warlock and Paladin, you normally want to progress the warlock more/faster than a paladin for increased spell slots.

Aura of Hate (Oathbreaker 7)

Aura of Hate
Starting at 7th level, the paladin, as well any fiends and undead within 10 feet of the paladin, gains a bonus to melee weapon damage rolls equal to the paladin’s Charisma modifier (minimum of +1). A creature can benefit from this feature from only one paladin at a time.

We'll use the Hexblade's Hex Warrior feature to use CHA instead of STR/DEX for our attacks:

Hex Warrior
When you attack with that weapon, you can use your Charisma modifier, instead of Strength or Dexterity, for the attack and damage rolls

Invocations are Devil's Sight, Improved Pact Weapon and Eldritch Smite (we want to smite as much as we can, since we're a paladin)

Fighting Style... so Blind Fighting is particularly interesting here because it frees up an Invocation if we want. Blessed Warrior might be useful for Guidance and Sacred Flame. Interception is unbelievable strong at low levels and you can swap it out if you're using the optional class feature Martial Versatility. Defense is boring but gets the job done.

Pact Magic

Pact Magic always affects your highest level spells...

Feats

Great Weapon Master

At this point, we're really just trying to make a meme out of the flat damage increase we have. We have +5 from Aura of Hate, we get +5 from Hex Warrior, our Pact Weapon gives us +1. Using GWM, we'll get an additional +10... So our Greatsword is +5 to hit for 2d6+21 damage (or +10 to hit, 2d6+11 damage).

I'm not convinced this is the best way to go by any means, but we're pumping up damage for fun. We should probably be looking for more reliable hits and using our Smites to deal damage.

More Options

We want to progress out character with spellcaster levels (higher level spell slots is better damage), so we want to think about what other CHA-based spellcasters offer.

Swords Bard gives us Sword Flourishes (more damage)... 3 levels in bard also gives us Silence

Sorcerer gives us some metamagic options and that plays well into the bard because we can give ourselves Subtle spells while we're in our own Silence pools.

Don't do Cleric, 8 levels for another way to Smite is weak (especially considering the multiclass requirements).

Is Improved Diving Smite worth it?

Improved Divine Smite
By 11th level, you are so suffused with righteous might that all your melee weapon strikes carry divine power with them. Whenever you hit a creature with a melee weapon, the creature takes an extra 1d8 radiant damage.

We're not going to get 18 levels in Paladin, so our Aura of Protection and Aura of Hate are only going to be 10 feet (that's probably a good thing).

I don't really think so. It's a free 1d8 damage on all of our attacks.. so it helps us keep up with Fighters getting a third attack at the same level. The problem here is that we want to make our attacks/smites as efficient as possible given we have limited resources. I'd rather ignore Extra Attack entirely and use cantrips like Booming Blade to supplement our damage. It's weird because the damage from Extra Attack doesn't scale into later tiers of the game but Booming Blade and Green-Flame Blade do.