The possible encounters on Route 1 are Caterpie, Hoothoot, Grubbin, Skwovet, Blipbug, Rookidee, Nickit, and Wooloo. This means for your playthrough, the fully-evolved Pokémon you can use are Butterfree, Noctowl, Vikavolt, Greedent, Orbeetle, Corviknight, Thievul, and Dubwool. I have experience using all of these Pokémon in SwSh playthroughs, so I feel qualified to answer this question.
Butterfree
Butterfree is noteworthy in the early game, with an early evolution and a strong matchup into Milo. In addition, it gets moves like Quiver Dance, Bug Buzz, Air Slash, and Psychic. However, due to its terrible typing and low defenses, it will start falling off once better Bug types become available.
Noctowl
Noctowl is okay. Deceptively high HP and Special Defense give it some bulk, plus it evolves at a respectable level. Strong STAB in Hyper Voice and Air Slash, plus interesting coverage options like Moonblast, Heat Wave, Psychic and Shadow Ball, make it able to handle a variety of opponents. However, its Defense and Speed leave a bit to be desired, so it might find itself in trouble in the midgame against foes like Gordie and Melony.
Vikavolt
Vikavolt is good. I mean, Vikavolt is really good. Phenomenal Special Attack and a fantastic Ability in Levitate, along with access to moves such as Bug Buzz, Thunderbolt and Energy Ball, make Vikavolt fantastic. It does fall short in defenses and Speed though, so it might take a bit of damage before it's able to OHKO.
Greedent
Greedent balances low Speed with high bulk. Its Attack is respectable and it learns diverse coverage moves (including Psychic Fangs for its Fighting weakness), so it can definitely hold its own. It's not the best Route 1 Pokémon, and it'll often be chipped down before it can attack, but at least it can hit back relatively hard.
Orbeetle
Orbeetle is generally inferior to Vikavolt. This is because its attacking stats aren't as high, its moves aren't as useful, and defensive Bug types aren't particularly helpful in-game. While it's still usable with moves like Bug Buzz, Psychic, Reflect and Light Screen, Vikavolt is typically the better Bug type.
Corviknight
Corviknight might be the best Route 1 Pokémon of them all. Steel/Flying is a fantastic typing that allows Corviknight to reliably wall a ton of opponents, and while its attacking stats are average, it learns all it needs: Iron Head, Brave Bird, U-turn, and Hone Claws. Its one issue is its late evolution level, but it comes just in time for the Fairy Gym and Corvisquire works fine until then.
Thievul
Thievul is fast and Nickit evolves early, but its attacking stats are paltry and its defensive ones aren't much better. It has access to some decent moves, but most are physical, going off its worse Attack. The best attacking moves it learns are Dark Pulse, Shadow Ball, Psychic and Grass Knot, so TR farming is practically mandatory.
Dubwool is a worse Greedent. It's tanky, especially with Cotton Guard, but it's not a great attacker. The best moves it learns are Cotton Guard, Body Press, Body Slam, Zen Headbutt, and Wild Charge. Fluffy is a good Ability, but ultimately Dubwool falls short of Greedent (which itself isn't anything to write home about).
In conclusion, some of the Route 1 Pokémon are much better than others. Below I've ranked them based on their general usefulness throughout the entire game.
- Corviknight
- Vikavolt
- Noctowl
- Butterfree / Orbeetle
- Orbeetle / Butterfree
- Greedent
- Dubwool
- Thievul
As you can see, Corviknight and Vikavolt are the top two choices that you should probably have on your team most of the time. Dubwool and Thievul shouldn't really be considerations, seeing as they're either outclassed or simply very weak.
