Vanguard

People misunderstand the Ranger when they say it could be replaced by the Druid version of the Eldritch Knight. The Ranger is a bundle of both mechanical and flavor aspects that could not fit into a single subclass of another class, and has an abundance of subconcepts that have not been explored in 5e yet that each deserve to be their own subclass.

A lot of amateur (and maybe some professional?) designers have an aesthetic distaste for the Ranger, since it is a##-backwards from the rest of 5e design. The subclasses are load-bearing and the core class is mainly flavor.

I'd say a lot of this has to do with how widely "physically-oriented wilderness survivor" varies in flavor. The Hunter is the true Ranger. Mechanically, it's a DPR-oriented long-rest class (and meant to occupy a space between the Fighter and the Rogue), just as the Monk is a DPR-oriented short-rest class. That's how it shines.

The history of D&D, however-- flavor-wise at least -- places Beast Master in bed with with the Ranger. How do you convey that? It can't be as strong as the Hunter and also have a beast. (Also, remember how 5e works -- what were separate but similar classes in other editions are bundled together as "Archetypes" in this edition.) So you put most of the DPR in the subclasses -- the subclasses other than the Beast Master.

A##-Forwards

The Vanguard is a proof of concept -- the concept that the Ranger occupies a unique role mechanically and flavorfully that the Fighter as stands cannot fill.

I will use some technology from Xanathar's Guide to Everything, The Mike Mearls Happy Fun Hour, and other classes to demonstrate this, by building like a normal class -- DPR-oriented and long-rest based.

Rural Ingenuity, or Flexibility

For the Ranger, far from the support of a huge and varied community, being to much of one thing is death. Too fragile and you die, too confrontational and you die, too mundane in a world of magic monsters and you die. I'll try to capture some of the same spirit.

Creating a Vanguard

See: "Creating a Ranger" in the Player's Handbook, but ignore the parts about particular hatred, and add some stuff about scouting ahead and supplying the party.

Class Features

As a vanguard, you gain the following class features.

Hit Points

Hit Dice: 1d10 per vanguard level

1d10 per vanguard level Hit Points at 1st Level: 10 + your Constitution modifier

10 + your Constitution modifier Hit Points at Higher Levels: 1d10 (or 6) + your Constitution modifier per vanguard level after your 1st Proficiencies

1d10 (or 6) + your Constitution modifier per vanguard level after your 1st Armor: Light armor, medium armor, shields

Light armor, medium armor, shields Weapons: Simple weapons, martial weapons.

Saving Throws: Strength, Dexterity

Strength, Dexterity Skills: Choose three from Animal Handling, Athletics, Insight, Investigation, Nature, Perception, Stealth, and Survival

Equipment

You start with the following equipment, in addition to the equipment granted by your background:

(a) scale mail or (b) leather armor

(a) two shortswords, (b) two simple melee weapons, or (c) a longsword and a shield

(a) a dungeoneer's pack or (b) an explorer's pack

A longbow and a quiver of 20 arrows

Handy

Your self-reliance has made you the master of a few skills. You learn one language and one tool skill of your choice. In addition, choose one of your skill proficiencies and one of your tool proficiencies. Your proficiency bonus is doubled for any ability check you make that uses either of the chosen proficiencies.

At 6th level, you can choose one more of your skill proficiencies to gain this benefit.

Marking Eye

Beginning at 1st level, your keen eye for detail makes you an unshakeable observer. You can use a bonus action to designate one creature you can see within 90 feet of you as the target of this feature. You have advantage on any Wisdom (Perception) or Wisdom (Survival) check you make to find that target, and on any Wisdom (Insight) check you make to discern its intention or predict or deduce its actions.

In addition, when you take the Attack action on your turn against a creature designated by this feature, you can make one additional weapon attack.

This benefit lasts until you take a long rest, lose consciousness, or designate a different creature with this feature.

Fighting Style

At 2nd level, you adopt a particular style of fighting as your specialty. Choose one of the following options. You can't take a Fighting Style option more than once, even if you later get to choose again.

Archery

You gain a +2 bonus to attack rolls you make with ranged weapons.

Defense

While you are wearing armor, you gain a +1 bonus to AC.

Dueling

When you are wielding a melee weapon in one hand and no other weapons, you gain a +2 bonus to damage rolls with that weapon.

Two-Weapon Fighting

When you engage in two-weapon fighting, you can add your ability modifier to the damage of the second attack.