So if you had to chose a pair skill that could really represent each of the current ranger subclass

some examples

Beastmaster animal handling or medicine

fey wanderer deception or persuasion

gloomstalker insight or stealth

hunter perception or survival

Gloomstalker i would go perception and stealth

Monster hunter perception or investigation.

I'm going to focus on theme, so there is no guarantee a Ranger of a given subclass will want the listed skills, because the subclass might be defined by making the skill redundant (like with Monster Slayer, for example).

• Beast Master:  Animal Handling, Nature
• Fey Wanderer:  Deception, Persuasion
• Gloom Stalker:  Perception, Stealth
• Horizon Walker:  Arcana, Athletics
• Hunter: Smith's Tools, Woodcarver's Tools (I know you asked for skills, but thematically the best fits for a Hunter would be what lets you make quarry-specific weaponry, like silvered weapons to hunt a werewolf or mistletoe arrows to hunt Baldr - and in 5E that's covered by tools, not skills.)
• Monster Slayer:  History, Investigation
• Swarmkeeper:  Animal Handling, Nature (in terms of theme, Swarmkeepers are Beast Masters where the Beast is a swarm - if Beast Masters could take e.g. bee swarms as their beasts, it would be even more obvious Swarmkeepers don't have genuinely unique flavor)
  • Bonus round: to avoid having two subclasses with the same thematic skills, you can gut the listed Swarmkeeper flavor and replace it.  Its mechanics are spot on for a Ranger whose power source is a powerful entity from the plane of Air, like a Royal Djinn.  If you reflavor it this way, Arcana + Nature.
• Drakewarden:  Insight, Nature (again similar to Beast Masters, only with the caveat that they specialize in sophonts to be reasoned with, not creatures with animal-level intelligence).

Arcana. So they can scribe their own scrolls.