Leo is a very natural and spontaneous actor, much like Amitabh Bachchan, who is also natural and spontaneous and he's been doing it for 56 years now. I'm very lucky to see his performance on set while working with him (the two are part of the much-delayed Uyarntha Manithan).
When it comes to actresses, I love Julia. Her heart reflects on her face. When you see her performance, you can see her heart. There is magic, and she's a magical performer. You need to see it to feel it. Till today, no one can beat her.
He has the diction of Sivaji Ganesan sir, yet gives a controlled performance with excellent range.
I was told that Marlon Brando and Anthony Hopkins, two actors who are very great in their journey, follow the same ideology that an actor should never have to try to remember the next line, but they act on it in different ways. I've heard that Marlon Brando always uses prompting. Sir Anthony Hopkins, on the other hand, never takes prompting, and both are rated as great actors. Brando says that if an actor has to think what his next line is, then he is not a good actor. For example, if there is a dialogue, most actors say the first half, take a pause, and say the second half of the dialogue. In that pause, they try to remember the next line. Brando says that you should not put in any effort to know your next line. It should come naturally. He uses prompters or sometimes boards.
Sir Hopkins, on the other hand, memorises his lines; they are part of his system. He breathes those lines. The point that both of them convey is the same: "I should not struggle for my next line". One actor takes the lines from outside and delivers it, and the other takes it from inside and delivers it.