favorite cartoon girl?

Azula <3

My most favourite would be Jenny from My Life As A Teenage Robot.

Honourable mentions: Ami from Hi Hi Puffy Ami Yumi, Patsy from Camp Lazlo, Panini from Chowder, and Lexi from Loonatics Unleashed.

Barbara Gordon aka Batgirl. She's one of my favorites in general

I think my fav, probably has to be Princess Sofia

By Cartoon, I'll take it as talking about Western Animation and excluding Anime. There are quite a few to mention nonetheless.

Harley Quinn is certainly one of them.

Others including:

Starfire from Teen Titans.
Gamora from Guardians of the Galaxy.
Charlotte Magne from Hazbin Hotel.
Ty Lee from Avatar: The Last Airbender.
Korra from Avatar: The Legend of Korra.
Rainbow Dash, Pinkie Pie and the Dazzlings from My Little Pony.
Star Butterfly from Star vs. the Forces of Evil.
Ahsoka Tano from Star Wars.
Bridgette, Lindsay, Zoey and Dawn from Total Drama.
Karai and April O'Neil from Teenage Mutant Ninja Turtles.
Miko Nakadai from Transformers Prime.
Lola Bunny from Looney Tunes.
Jenny Wakeman from My Life As A Teenage Robot.
Jinmay from Super Robot Monkey Team Hyperforce Go!
Go Go Tomago from Big Hero 6.

Those in particular among others !!!!

Yi (Abominable)
Kagami & Lila (Miraculous)
Katara, Toph (The last Airbender)
Claire, Aja, Nomura (Tales of Arcadia)
Merida, Mulan, Judy Hopps, Belle, Maid Marian (Fox), Princess Jasmine (Disney movies)

Toph!

Rayla from The Dragon Prince! <3

Elsa.