How does the troop counter triangle work (who beats who)?

The 4 troop types counter each other in a loop. The wheel to remember:

Cavalry → beats → Shields → beat → Archers → beat → Spearmen → beat → Cavalry (and back round).

In plain terms:

• Cavalry beats Shields
• Shields beat Archers
• Archers beat Spearmen
• Spearmen beat Cavalry

Siege is weak against every type, but deals extra damage to durability (the HP of tiles and structures).

The advantage gives +7% to the one who has it and −7% to the one who suffers it: a 14-point swing, applied to every single hit, for the whole fight. That's no detail — it's one of the steadiest multipliers in the game.

The trap is elsewhere: the enemy type is often unknown (beasts, knights, big tiles, and your opponent in PvP). Picking your troops to counter something you haven't seen is a low-expectancy bet: a solid army beats a well-typed one. But the moment you can see the enemy's troop — a scout, a tile, a battle report — take the one that beats it: there, the 14 points are yours.