Heroes when attacking

Selecting the right heroes is one of the keys to a successful attack. Make sure that:

• you have at least 4 heroes of the troop type you're attacking with, so that your 4 main squads get their hero's Squad ATK;
• you maximise the ATK of the troop type you're attacking with (then HP, then DEF).

Given the list of available F2P heroes, we can come up with the best war teams depending on the troop type you're attacking with.

Infantry

Choose at least 4 INF heroes, maximise INF ATK:

• Soul Forger: INF hero, brings INF ATK
• Sea Squire: INF hero, brings INF ATK
• Demon Slayer: INF hero, brings INF ATK and INF HP
• Oath Keeper: INF hero, brings INF ATK and INF HP
• Then either Rose Knight (CAV hero): brings ARMY ATK
• Or Bombin' Goblin (RNG hero): brings ARMY ATK too

Ranged

Choose at least 4 RNG heroes, maximise RNG ATK:

• Tracker: RNG hero, brings RNG ATK
• Death Archer: RNG hero, brings RNG ATK
• Snow Queen: RNG hero, brings RNG ATK and RNG HP
• Bombin' Goblin: RNG hero, brings ARMY ATK
• Then Rose Knight (CAV hero): brings ARMY ATK

Cavalry

Choose at least 4 CAV heroes, maximise CAV ATK:

• Night Raven: CAV hero, brings CAV ATK
• Child of Light: CAV hero, brings CAV ATK and CAV HP
• Rose Knight: CAV hero, brings ARMY ATK and CAV HP
• Death Knight: CAV hero, brings CAV HP
• Then Bombin' Goblin (RNG hero): brings ARMY ATK

Side notes

Leader

When attacking, make sure one of the selected heroes is your leader, otherwise, your gear and talents won't apply.

Given the above lists, we can see that Rose Knight or Bombin' Goblin are good candidates for being your leader, as they end up in all battalions, meaning you won't have to change your leader before attacking (which can be easily forgettable). Those two should also be stationed on your wall anyway.

Event and P2P heroes

If you have event or P2P heroes, you can obviously use them instead of the ones listed above: just make sure you end up at least 4 heroes of the troop type you're attacking with, and that they help to maximise the ATK (for example, a legendary Rose Night is still better than a common Watcher).