Black. She doesn't actually like it black, she just thinks she should because she's the edgy member of the group.
Beast Boy has a onions latte, no sugar.
Stafire unironically likes those disgusting sugary things that people make for Instagram, but she'll add unrelated condiments to them if she finds them laying around.
Jinx also enjoys extremely sweet colorful drinks, but goes out of her way to hide this.
Cyborg prefers energy drinks.
No idea what Robin would like.