Haven

Regular heroes
Rutger - usually very useful as a secondary hero, also interesting on bad terrain.
Vittorio - on a medium map, but good against a chaos player. In other cases, not so much. Though, against the AI he will perform well even on large maps.
Meev - a useful hero, quite strong in the late game. In her case, it is worth taking Inquisitors, as her specialization also applies to them.
Laszlo - one of my favorite heroes. Zealots can effectively take down various high-level melee units even in the early stages of the game, and earlier on, the starting Fortitude sharply extends the life of Peasants and Archers. In the endgame, Zealots are also hard to kill, unlike some of Dugal's shooters, and they hit quite hard.
Ellaina - like Rutger, useful as a secondary hero. As a primary, she might work out if there are many Peasants and you can gather various buffs for them: life rings, Blood Claw necklace, Battle Frenzy, Fortitude + something for speed. That's the ideal.
Dugal - good on small maps. On large ones, he is not as effective.
Axel - conversely, fits well on large and gold-rich maps.
Iris - because griffins are absent from the Knight training chain, it is not always possible to make them a dangerous stack. In my opinion, the choice in her favor depends more on the map.

Scenario heroes
Frida (wind-runner) - same as Meev, but with Tactics instead of Leadership. I don't see any major differences.
Godric - at first, Prayer works quite effectively, but later it yields to Meev. He also has +1 perk.
Isabelle (suzerain) - a very useful ability to reduce retraining costs, which can remove the Knight's terrible dependence on gold. The combination of Axel (possibly with Mentorship) + Isabelle looks interesting.
Glen = Vittorio.
Geir = Axel.
Nicholas ≈ Isabelle, but possesses Skilled Counterattack, and therefore is more useful.
Duncan - a Pathfindner with Tactics, a strange combination; Rutger looks better.
Ornella - a Pathfinder with troop gathering. Exclusively a secondary hero.
Frida (Vessel of Elrath) - a useful feature to avenge the enemy army without an extra action, albeit randomly. It might slightly interfere with resurrection during a breakthrough. The frequency of vengeance will be off the charts if you take Empathy and cast General versions of spells.
Ghost = Godric.
Isabelle (favorite of the gods) - although she has no skills at the start, the General, permanent, and irreducible Divine Strength is a strong argument in itself. If you manage to get Light early, the shooters will deal damage better than Dugal's. Of course, when choosing upgrades, you should pay attention to Royal Griffins, Knights named after her, and Fallen Angels as possessors of higher max damage stats.
Alaric - has Meev's specialization, but is much more useful than her due to having Battle Frenzy and Skilled Attack. That is, Peasants alone get +130% damage. At level 2, Alaric will be offered Haste, and with proper luck, Retribution can be taken at level 3-4. In general, troops start biting hard from the very beginning of the game, which allows setting the necessary pace of development. The main thing is to set hero movement speed to maximum.
Laszlo (red) - instead of Defense and Fortitude, he has Attack with Tactics; the build will be worse than white Laszlo.
Andrias = Vittorio.
Lorenzo = Dugal.
Valeria = Axel.
Benedict - has developed Logistics instead of Pathfinding like Rutger. Plays better on good terrain, although by level 2 they may lose their differences entirely.
Bertrand - the same as Laszlo, but instead of Fortitude he has Evasion, which usually plays weaker.
Orlando - a griffin trainer with a clean biography and skill tree, and therefore not interesting.
Gabriel - also a trainer, but with basics of Leadership and developed Counterattack.
Saint Isabelle ≈ Isabelle (suzerain), but with 4 points of Knowledge.