Which of these actors who played in a Best Picture Winner for the first time during or after 1970 is your favorite?
Can you rewrite or clarify your question? Are you asking about actors whose first role is a Best Picture Winner? Because that idea doesn't directly translate into your question as written. Or are you asking something else? Assuming that this also can be said about your pre1970 version of the suggestion.
And can you please add the title of the Best Picture which each actor has said to acted in in their respective text boxes?