Understanding film and film scripts is really essential. Especially for dialogue and how it works. Moreso than novels.
But novels are great for story and for narrative. And keeping narrative prose fresh.
Man, you really need to read everything.
Are we talking about for craft or for inspiration? For craft, you definitely need to be reading all kinds of fiction. For inspiration, I think it really helps to look at non-fictional stuff, like news and history. If you want to create fiction that isn't just based off of rehashed versions of the Dark Phoenix saga or Pulp Fiction, then you need to be looking for material. Talking to friends, interacting with people, that's all really good. Look for stories in your friends. But there's also news. And if you're a high concept writer, that's especially key. Scientific news. And historical events. Historical figures and situations.
My film, Bad Habits, was based off of real interaction between an 18-year-old and his social worker, as heard on NPR during my commute.
My sci-fi script, The Maitland Exhibit, was based off a discussion with friends (back in 1999) about what would happen if the record industry DID crumble because of Napster.
My comics script Vostok is based on a real lake in Antarctica. That springboard was...OK, if it's a one-way trip, who the hell would go there?
So, that's what I'd say. Study action, visual storytelling and dialogue from film. Study comics-specific storytelling (panel structure, etc.) from really good comics. Study narrative and prose from novels. And then go find stories from the real world.