There are 40 different Dark-type Pokémon in Pokémon Scarlet and Violet, and 'which ones are the best' is a tricky question to answer. Strong against Ghost-types and immune to Psychic-types, Dark-type Pokémon generally have a good balance of HP, Attack, and Speed, although their weaknesses to Bug-, Fairy-, and Fighting-types do make them a bit situational. This Type-category has many additions to any trainer's team.
While 40 may not seem like a lot, there's a one-in-ten ratio for all 400 Pokémon currently available in the Paldea region. As a result, players will be stumbling across Dark-types often, either in the wild or under other trainers, and should be spoiled for choices even when trying to do a Nuzlocke run in Scarlet and Violet.
Strongest Dark-Type Pokémon in Scarlet and Violet
The first and most prominent of the Dark-types are the Four Treasures of Ruin. Wo-Chien, Chien-Pao, Ting-Lu, and Chi-Yu are all dual-type Pokémon with Dark-type as their primary typing and 570 total stats. However, a player can only catch one of them per game. Chien-Pao is the best amongst the four, thanks to its monstrous combination of high Attack, higher Speed, and an ability -Sword of Ruin- that decreases the Defense stat of other Pokémon. Its dual Dark-/Ice-type gives it several vulnerabilities, and it will die to any Fighting-type that can get a hit off, but it's so fast that it just needs the right build in Pokémon Scarlet and Violet.
Next on the list is a returning classic, Umbreon. The toughest of the Eevee evolutions, Umbreon has an incredibly high Defense and Special Defense, allowing it to withstand attacks while chipping away the health of enemy Pokémon. The only fundamental flaw is its low offensive stats, but the Same Type Attack Bonus for Dark Pulse and Assurance let it bridge the gap, and that's not counting potential TM moves.
Last but from least, there's Kingambit. A Dark-/Steel-type, this lordly Pokémon has nine types of resistances and unfairly high Attack and Defense stats. But, according to the Youtube channel ArekkzGaming, it gets more ridiculous when a player combines its ability, Supreme Overlord, with its signature move Kowtow Cleave, making the hassle of evolving Bisharp into Kingambit well worth it. The first ability increases Kingambit's attack damage by 10% for each fainted Pokémon in the party while the second move only misses when moves like Dig or Fly are used in Pokémon Scarlet and Violet.
Source: YouTube/ArekkzGaming