I do not play Warhammer but understand the basic mechanics, asked the computer for a top pick, and then searched YouTube.
This video ranks all Space Marine units for usefulness in 2026: Every Space Marine Vehicle Unit Ranked - Best Tanks and Dreadnoughts in the Codex in 2026?
The nice thing about this video is that it ranks all the units, so you can see a bunch of the top hitters. The maker raked the Vindicator as the best all around unit. It is 185 points.
When I asked the computer, it came up with the Repulsor Executioner. This unit costs 220 points and ranks in 5th place in the linked video.
So, in Warhammer, each player is given a number of points with which to buy military units. Once everything is purchased, the players duke it out. This is a very standard setup system for war games. The higher the cost of a unit, the more powerful it is. However, players often find that lower cost units offer more utility than higher cost ones.
This is no doubt why the person who made the video above ranked the Vindicator (185 points) above the Repulsor Executioner (220 points). In the video above, at 6th place. there is an even more powerful unit, the Land Raider Redeemer (270 points).
If you want “Best” based on points, it looks like Land Raider Redeemer is your winner. If you want “Best” based on a compromise between cost and firepower, Repulsor Executioner may be the best pick. If you want “Best” based on point cost efficiency, Vindicator may be your choice.
Warning. If you ask 10 players of a war game what the “Best” unit is, you will often get 10 different answers. As a former player of many war games, the only way to really know “Best” is to play them all and work out the best tactics versus people in the local group of available players. Sometimes, the “Best” option is driven by factors other than point cost. For example, other players may not understand the rules governing a specific unit and therefore be very vulnerable to it.
Oh. One final metric of “Best” is looks. Do not dismiss this form of “Best”. I had a lot of friends who made all sorts of compromises to fit cool looking “Best” units into their formations.
Edit: Whoa! I watched that whole video and it turns out there are two even more expensive units, the Thunderhawk at 840 points (a flyer) and the Astraeus at 525 points (a super tank). The video maker ranked them very low for point efficiency. The Astraeus is the biggest tank in the video but the video maker said it may be too big for most maps. A map is the terrain units are deployed on for play. Imagine a huge diorama with lots of blown up buildings, rocks, and junk scattered about. That is a map.