Well let's take a look at each starter:
QUAQUAVAL:
Pros:
- High attack
- Aqua Step to increase Speed
- Powerful attacks
-Wide movepool
Cons:
- Pretty annoying to use early on
- Slower in-game play
- Not great facing Gym Leaders
Good against:
- Gym: Larry
- Star Bosses: Giacomo, Mela, and Eri
- Titans: Klawf, Orthworm
- Elite 4: Rika
- Other: Nemona
Okay against:
- Gym: Katy, Ryme, Grusha
- Star Bosses: Atticus
- Titans: Bombirdier, Iron Treads/Great Tusk
- Elite 4: None
Bad against:
- Gym: Brassius, Iona, Kofu, Tulip
- Star Bosses: Ortega
- Titans: Dondozo/Tatsugiri
- Elite 4: Poppy, Larry, Hassel
MEOWSCARADA:
Pros:
- Fast
- Guaranteed critical hits with Flower Trick
- Wide movepool
Cons:
- Frail
- 7 Weaknesses
- Grass isn't generally a great offensive type, which is how Meowscarada is built
Good against:
- Gym: Iona, Kofu, Tulip, Ryme
- Star Bosses: None
- Titans: Klawf, Dondozo/Tatsugiri
- Elite 4: None
Okay against:
- Gym: Brassius, Larry
- Star Bosses: Eri, Giacomo
- Titans: Orthworm
- Elite 4: Rika, Hassel (if you have Play Rough)
Bad against:
- Gym: Grusha
- Star Bosses: Mela, Atticus, Ortega
- Titans: Bombirdier, Iron Treads/Great Tusk
- Elite 4: Poppy, Larry
SKELEDIRGE:
Pros:
- Current greatest offensive types
- Torch Song to increase special attack while attacking
- Decent bulk
Cons:
- Slow
- Shallow movepool
Good against:
- Gyms: Katy, Brassius, Larry, Tulip, Grusha (Skeledirge turns this fight into a joke with Torch Song)
- Star Bosses: Giacomo(Skeledirge won't have Ghost typing yet)
- Titans: Orthworm
- Elite 4: Poppy, Larry
Okay against:
- Gyms: Iono, Ryme
- Star Bosses: Mela, Atticus, Eri
- Titans: Iron Treads
- Elite 4: None
Bad against:
- Gyms: Kofu
- Star Bosses: Ortega
- Titans: Bombirdier, Great Tusk, Dondozo/Tatsugiri
- Elite 4: Rika, Hassel
FINAL NOTES:
Each of these Pokémon starters have their own strengths and weaknesses. They were made with different uses in mind and can't really be judged by who's best in this case. However, Skeledirge is perfect to speed up progression. Torch Song allows you to setup while attacking, decreasing the amount of battle time. Decent bulk allows Skeledirge to take less trips to the Pokémon Center. With a speed investment and the usual few level advantage, you can outspeed most other Pokémon, which means you'll be taking less damage. I would choose Skeledirge for faster gameplay, but the choice is really yours. There's no huge disadvantage or advantage of choosing one starter over the other. I hope this helped you!