It was tough call with a few more people to choose from than 1, but I ultimately decided to go with @braveheart29.
Her and I met around the time I joined Steemit, and she proposed I write a story with the title "Slaughterhouse". After I did, she asked me if I could write another part, and sooner than you know it, we're 13 parts down the line, each writing one part of the story.
I chose her because she motivates me to write and create, and because she always presents me with new challenges with her parts of the story (If you wish to read it, click here). I was never good at writing anything longer than short stories of max 1500 words, but with her help, we are writing a lengthy story together! :D And I even noticed I can write longer stories myself! :D (Managed to write one around 8000 words long. I believe it's safe to say I wouldn't have embarked on that journey had I not been collaborating with @braveheart29)
She made Steemit not just fun for me, but a healthy challenge also, that helps me improve as a writer and keeps me motivated.
Also, she's a very kind person I have had many interesting conversations with.
She's a fellow qurite also ^^

Thank you for this amazing initiative @raised2b!