Blood Bound: 

Bloodseekers are extremely strong early on and can help you snowball the game, but they fall-off a bit in the late game when tankiness (Warrior, Kight, Brawny) and strong CC (Tide, Break effects) start kicking in.

Bloodseeker builds are absolutely devastating in lobbies with squishier strats and Summoners.

Blood Bound are a bit more complicated in Knockout because you cannot run multiple low-star heroes of the same type without combining them to a three stars, so you have to rely on a three-star BS carrying you, which might become problematic in the late game.

BB strats are extremely powerful as a whole but aren't the most reliable ones because they are very item dependent - the Ogre Hat and at least one of the Stonehall items for your Bloodseeker(s) provide a big boost in power.

Heartless:

(2) Heartless is very easy to get and almost mandatory for all physical damage builds.

(4) Heartless is the most common damage-boosting Alliance right now as it works very well with most damage-dealing heroes. The most common strategy is (4) Heartless (3) Warriors (3) Hunters, but other variations are also viable.

(6) Heartless is also strong but not S-tier - it's much harder to get and leaves too little space on the board for strong damage dealers.

Hunters: (3) Hunters are S-tier because of how great they work with Vigilant, Warrior, and Heartless Alliances, making them the default damage-dealing backline.

(6) Hunter drafts aren't doing as well comparatively since the removal of the Medusa Ace effect, but they are still quite good. In Standard, it's a bit harder to make them work because you have frontline problems, but in Knockout, they are one of the strongest strategies. This happens because having multiple three-star Hunters (quite easy in KO and impossible in Standard) gives you an obscene amount of damage from the start of the round.

Warriors: (3) Warriors are the best frontline once again since the reintroduction of Tide: Tide + Slardar + 1 gives you a frontline with high armor and great control in addition to more magic resistance for your whole lineup hanks to (2) Scaled.

(6) Warriors are not bad but they are not S-tier - they don't deal enough damage and the armor isn't sufficient to give them the win in most cases. E.g. (6) Knights is a better tanky draft right now.

Vigilant: the recent change (+50% damage on the first hit on a new target) took the Alliance from F to A tier. It works extremely well with Hunters (and the ease to get at least two or three Vigilant is a big reason Hunters are S-tier right now).: the recent change (+50% damage on the first hit on a new target) took the Alliance from F to A tier. It works extremely well with Hunters (and the ease to get at least two or three Vigilant is a big reason Hunters are S-tier right now).

Knights: they suffer a bit from the loss of the 4-cost Dragon Knight, but they more than compensate from the reintroduction of Luna into the Knights roster. She is by far the most important carry in the build and your top three-star priority. She is great against Summoner builds and Knights as a whole are good against Bloodbound Bloodseeker comps.

Knights work very well with (2) or even (4) Healers and one of the healing Underlords (healing Enno and Anessix) because they are quite durable and tank together (which means heroes don't get bursted down one by one).

Spirits: three Storm Spirits + (3) Mages + (3) Spirits is still an extremely powerful build and it's pretty common in high-level lobbies. It works by abusing Delta Slam to the max by including as many Spirits as possible in addition to the (3) Mages and (2) Human bonuses to make their damage stronger.

That said, its a bit harder to build compared to the (4) Savage builds and a much, much lower tier in Knockout where you simply cannot have multiple two-star Storm Spirits.

Brawny: (4) Brawny builds are S-tier in Knockout mode because it's easy to get four Brawny heroes fast while also getting some of them to two and three stars extremely quickly, allowing them to accumulate a lot of kills and an ungodly amount of bonus HP.

In Standard mode, they are still very good, but it's harder to get multiple Brawny heroes on a high level fast enough to get an "imba" amount of kills. Moreover, they are vulnerable to Kaden's blade and the (4) Savage bonus.

Assassins: Assassins are not S-tier, but they are definitely in a very good place right now. A (6) Assassin + (3) Void lineup does very well against most top-tier builds: they counter healing and high health (Brawny, Warlock, healer Underlords) and they quickly nuke-down squishy backline damage dealers (most importantly Hunters). That said, they are much more upgrade-reliant compared to the S-tier builds.

This upgrade reliance means they usually do well in Knockout.

Druids: (4) Druids are very rarely used, but (2) Druids are a must in almost all Savage comps and in a lot of other decent builds (e.g. Champion builds, Summoner Builds, etc.).

Treant + 1 Druid carries the early game (Seed is still extremely good), while later on Lone Druid shines with the Savage bonus and his powerful Bear summon, which even benefits from the Summoner Alliance bonus.

Champion: builds fully designed to make Legion Commander the main carry (with plenty of two-hero Alliances) are still decent. Combine her, most importantly, with (2) Brutes, (2) Druids, a Demon, and ideally (2) Trolls and (2) Knights.

Warlocks: in a good place right now because they work very well with tanky strategies (especially (4) Brawny). Moreover, the (2) and (4) Healer change is also an indirect buff to Warlock comps.

That said, the loss of the Disruptor Ace bonus hurts them and full Warlock comps are much worse than before. In the current meta you usually want to run between two and four Warlocks as a secondary synergy.

Warlocks work very well with healer Jull because they heal him very efficiently and he becomes one of the most unkillable units in the game.

Healer: from the weakest Alliance in the game, (2) or (4) Healers became quite powerful because they are easy to get and they synergize extremely well with the Underlords. They are important if you are running Warlocks and/or one of the healing Underlord variations.

Brute: very good in the early-mid game, but suffers in the late game especially versus the top-tier builds. That said, (4) Brutes work very well with (4) Heartless and  (2) Brutes are very important in Champion drafts.

Also, a three-star Lifestealer with a good item shouldn't be underestimated. A full (4) Brute draft is much better in KO compared to Standard because of this reason.

Scaled: We put it in B-tier simply because this is not a Mage meta. That said, the reintroduction of Tide means (2) Scaled is very easy to get in most lineups and is quite useful in most cases (just not game-breaking).

Trolls: (2) Trolls is quite often used (especially with Knights), but (4) Trolls is a bit hard to fit into the current meta. (4) Trolls (6) Knights is the best option by far but still requires a 5-cost here (Troll Warlord) to reach its full potential.

Mages: (3) Mages is a very important part of the Spirits build, but (6) Mages is quite hard to pull-off in the current meta. Scaled is very easy to get and most good builds demolish a full Mages draft in the mid game.

Dragons: suffers from the move of Dragon Knight from tier 4 to tier 5 and are much less common in Knights, where they were most commonly used in the past. That said, (2) Dragons are a key part of (4) Brawny strategies because a Snapfire with the Dragon bonus deals great damage and gets kills extremely quickly.

Summoner: (2) Summoner is easy to get and somewhat important if you have Lone Druid. Full (4) Summoner drafts, however, are very vulnerable to AoE damage (Knights with Luna) and provide Bloodseekers with a source of endless heals (one of the biggest reasons Bloodseeker drafts are S-tier). Last but not least, (4) Summoners require Nature's Prophet, who's arguably the weakest hero in the game right now.

Void: very hard to get early on which means it's not the most impactful bonus, but once you get it in the late game it's quite decent. It's a good addition to Assassins especially when you are fighting against Brawny lineups, but it's not an Alliance bonus you build a whole strategy around.

Savage: The best Savage strategies right now are (4) Savage (4) Summoner and (6) Savage + (3) Hunter. That said, they are not imba, and they suffer from the meta a little bit. Summoner is still vulnerable to Bloodseeker (less than before) and AoE control/damage, while (6) Savage + Hunter builds are strong on lvl9-10 but suffer a bit in the mid game.

Demons: one Demon is good to have in a lot of drafts and extremely important in Champion builds. Multiple demons are harder to pull-off and are usually viable only with Terrorblade + Legion in the team.

Multiple Demon strategies are much, much better in KO compared to Standard because multiple three-star carries (Legion, Terrorblade, Chaos Knight) make Demon builds a lot stronger.

Humans: After the rework, Humans simply became an extension of the Mages bonus. They are extremely important in Mage strategies and quite unimportant in most other builds. (2) Humans is great to have if you rely on spells, (4) Humans is usually an overkill.

Deadeye: it matters only for Bloodseeker since the removal of Gyro and Sniper, so you might as well ignore it.

Primordials lost their (6) hero bonus and Ace effect, which made the Alliance irrelevant in the late game. They are alright early on, but you simply never build for the late game with Primordials in mind.