I am thinking best are:
19/1 - CHA SAD, shield, curse etc. Full Paladin progression and slots. 5th level Paladin spells.
18/2 - Agonizing Blast + Devil Sight. But you lose one 5th level slot. 5th level Paladin spells.
17/3 - Darkness and 2x 2nd level slots (3k8 smites). No more slots lost vs 18/2. 5th level Paladin spells.
But I wonder if you think the following could be more potent:
11/9 - You get Improved Smites, 3rd level spells and 2x 5th level short rest slots by level 18. We could also go 13/7 but in order of 1-6 Pal/1 Hex/7-11 Pala/12-18 Hex/18-20 Pala.
What do you think is most potent split. I don't like 6/14 as you get so few slots to use and Lifedrinker comes so much later than Improved Divine Smites.
RestPaladin spell slots short rest table

Short Rest Spell Slots 5e

Paladin

Short Rest Spell Slots Paladin

Spell slots for a tier 1 paladin are in short supply, and since Divine Smite kicks in when you hit a creature with a melee weapon attack it means the spell slot will never go to waste. This creates an unfortunate circumstance of leaving the paladin’s pretty nifty spell list kind of flat. Jan 22, 2016  The true synergy power between the Paladin and Warlock is the Paladin's smite and the Warlock's ability to regain spell slots each short rest allowing the paladin to use Divine Smite quite often. This build requires a minimum Paladin level of 2, and the first level should be taken in Paladin. Dec 11, 2019  As an extra bonus, he can use his Pact Magic slots to cast paladin spells and his Spellcasting slots to cast warlock spells. He also can regain his Pact Magic slots on a short or long rest as before, but his Spellcasting slots only recharge on a long rest.