For me it's a mix between Katarina and Fizz. I love my assasins with high mobility. Should be pretty easy to guess why these two are my favorite.
High HP bruisers. I like to be a threat, be in the middle, and make life hard for the enemy. Nasus is my favorite champion in league. For his versatility in roles and his ability to stay a relevant threat in a teamfight, he is my champion of choice. Shen is a close second, with his Taunt gap closer, his ability to split push and be a global threat, and his ability to heal up the team based on his HP with his Q.
Diana gotta be my favorite. My Christmas wish would be for her to come back into meta. First main champ was Jax though, so there is always a soft spot for the Grandmaster of Arms in my heart (Pre-Rework was better, Miss you Dodge runes)