Totally depends on the game and the genre, I don't have any specific ratio.
Game is first person? Mouse and keyboard.
Does the game improve by having better camera movement / aiming? Mouse and Keyboard.
It really depends if the game benefits from fast camera movements, and if it requires aiming. If it's a game using auto lock system like Guardians of the galaxy or Red dead redemption 2, I will use a controller. I also use a controller for melee games that don't require any aiming, like Kingdom Hearts, Bayonetta etc...
There are a lot of games that really benefit from mouse and keyboard though, even some that you might not suspect at first.
Sunset Overdrive is a great example, I never thought I would like this game that much, because all the videos I can find of it looks really slow and boring, but playing it with mouse and keyboard totally transforms the game, because the whole traversal gameplay is based on the camera position, and the mouse movement let you move much more freely and faster. If we stay in a similar genre though, I play Tony Hawk games with a controller, because you barely move the camera yourself in this game, you don't need improved camera controls, it doesn't affect the gameplay.
I often feel like I have more freedom when I'm playing with mouse and keyboard, it feels like having shackles being removed, it's smoother and faster, I'm not limited by the static speed of a stick, but some games do feel better with a controller if you don't need that increased freedom of camera movement.
