What are the strongest competitive lists going in Warhammer 40k at the moment, and why?

As of the latest tournament results and meta analyses for Warhammer 40k 10th edition, here are some of the strongest competitive lists and the reasons behind their success:

Astra Militarum (Imperial Guard)

• The Astra Militarum has been consistently strong, particularly with the release of new codexes and balance updates. They have dominated several recent tournaments, such as the Frost Spite GT and Everwinter Winter Assault, often going undefeated or with a single loss12.
• Their strength lies in their versatility, durability, and ability to field large numbers of troops, making them effective at holding objectives and wearing down opponents.

Adeptus Custodes

• The Adeptus Custodes have also shown significant strength, with multiple first-place finishes in tournaments like the Glass City GT and Defcon. They boast high win rates and total battle points12.
• Their power comes from their elite units with high durability and damage output, as well as their ability to score objectives effectively.

Necrons

• Necrons are highly competitive, with strong showings in various tournaments, including the LVOCan’t-Go and the Hamburg Major 2025. They have a high win rate and are frequently seen in top placements14.
• Their strength is in their durability, precision shooting, and ability to control the battlefield with near-indestructible units. Recent lists have leveraged these strengths to great effect, despite some nerfs to their best detachments34.

Adeptus Astartes (Space Marines)

• Space Marines, particularly the Ultramarines chapter, have seen a significant rise in competitiveness. They have a high win rate and are well-represented in top tournament placements. Units like Ballistae, Dreadnoughts, and Vindicators are staples due to their damage output and defensive profiles3.
• Their success is attributed to the versatility of their detachments, such as the Vanguard and Ironstorm, and the effectiveness of units like Intercessors and Inceptors in scoring objectives.

Thousand Sons and Other Factions

• Thousand Sons have had notable wins, such as Mattias Lindvall-Östling's first place at the Ironbound V tournament. This faction benefits from powerful psychic abilities and durable units1.
• Other factions like Deathwatch, Death Guard, and Dark Angels also show promise, with innovative lists and strategies that leverage their unique strengths. For example, the Death Guard have risen in performance after initial balance updates, and the Dark Angels have shown strong results in tournaments like the Hamburg Major 202514.

General Trends

• The current meta is characterized by frequent updates and new codex releases, which have introduced new detachments and strategies. Lists that can adapt quickly to these changes and leverage the latest rules and units tend to perform better25.
• Durability, precision shooting, and the ability to control and score objectives are key factors in the success of these competitive lists.

Overall, the strongest lists are those that can balance durability, firepower, and strategic flexibility, often leveraging the latest updates and codex changes to their advantage.