Ranger: A hardened fighter, doesn't use magic and focuses on mobility and exploration. I avoided damage features because I think the champion and Battlemaster should cover this better and being a fighter he is already better than a ranger fighting.
Lvl 3: Natural explorer: Proficiency bonus (or advantage if you don't like it) to survival, athletics, stealth, constitution (terrain & environment effects) and initiative checks in a terrain you know. Add a new terrain at lvl 7, 10, 15 and 18.
Steel will: Advantage on saving throws against fear
Lvl7: Land's stride: +10' movement
Lvl 10: Escape the horde
Lvl 15: Evasion
Lvl 18: Uncanny dodge
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Beastmaster: A fighter who fights with an animal companion, can cast spells to summon animals, cure, transform into an animal, etc.
Lvl 3: Spellcasting: Use Eldritch Knight's table, Spellcasting ability like ranger (wisdom)
Animal Companion
Lvl7: Irreductible companion: AC's HPs=6x fighter lvl and always heals the maximum of the dice, second wind also heals the AC 10+fighter lvl hps, when you spend hit dice to regain hit points the AC also heals (10+AC con).
Lvl10: Exceptional training: As the book + AC gets proficiency to all saving throws and 3 skills.
Lvl15: Bestial Fury
Lvl18: Share spells: As the book, also works for spells from others.
Spells:
Lvl 1: Alarm (animals), Animal friendship, Cure wounds, Detect poison and disease, Longstrider, Speak with animals,
Lvl 2: Animal messenger, Barkskin, Beast sense, Darkvision, Lesser restoration, Locate animals, Protection from poison
Lvl 3: Conjure animals, Dominate beast (10min, 1h lvl4), Protection from energy, Water breathing
Lvl 4: Freedom of movement, Polymorph (self only, animal form), Stoneskin
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All subclasses get 2 things at lvl 3, but the Champion only one that is random, with this he covers the durable fighter better:
Lvl 3: Improved second wind: 10 + Fighter level + CON modifier.