War heroes

This page lists the available F2P heroes, and flags the ones that are good candidates for being sent into battles.
See the best heroes when attacking and heroes when defending to find out the best teams of F2P war heroes.
Infantry heroes
With INF ATK
Soul Forger, aka Drumyr
Sea Squire, aka Lockfin
Demon Slayer, aka Shroud (brings INF HP too)
Oath Keeper, aka Wesley (brings INF HP too)
Remaining INF heroes
Scarlet Bolt, aka Greta
Shade, aka Blink
Ranged heroes
With RNG ATK
Tracker, aka Boom-Hilda
Death Archer, aka Cathiss
Snow Queen, aka Alice (brings RNG HP too)
With ARMY ATK
Bombin' Goblin, aka Tinkus
Remaining RNG heroes
Trickster, aka Tattler
Black Crow, aka Chadra (brings RNG HP though)
Cavalry heroes
With CAV ATK
Night Raven, aka Icarus
Child of Light, aka Sparky (brings CAV HP too)
With ARMY ATK
Rose Knight, aka Joan (brings CAV HP too)
Remaining CAV heroes
Death Knight, aka Shane (brings CAV HP though)
Sage of Storms, aka Anderson
Additional notes
Event heroes
Some heroes can be obtained only via events. Technically, they are F2P, but in practice, you need either time or money to get them up to legendary grade:
Boommeister, aka Manfred Brandt: RNG hero, brings ARMY ATK, ARMY HP and ARMY DEF as passive skills, i.e. they apply even if the hero isn't deployed (in other words, you don't need to send him into battle).
Chaos Dragon, aka Gravios: CAV hero, brings ARMY ATK and ARMY DEF.
Watcher, aka Deeproot: INF hero, brings ARMY ATK and ARMY HP.
P2P heroes
The above lists don't take P2P heroes into account, but as you can guess, most of them bring great ATK boosts.
ARMY ATK
Some heroes bring ARMY ATK: this applies to all the troops you're sending, whichever their type. For instance, if you have INF ATK 80%, RNG ATK 80%, CAV ATK 80%, and you're selecting a hero that brings 20% ARMY ATK, it ends up as if you had INF ATK 100%, RNG ATK 100%, and CAV ATK 100%.
ARMY ATK heroes bring less ATK than specific troop ATK heroes (20% vs 30% at legendary grade), but those heroes are still very useful to complete your selections when attacking or defending.
Siege heroes
Here are the siege heroes as a matter of completeness, but there's (almost) no point choosing any of them when fighting:
Elementalist, aka Rasmus
Incinerator, aka Monica
Prima Donna, aka Felicia