Nicholas Hoult is most notably known for his role as the blue shaggy-haired mutant, Beast from the X-Men comics/movies (X-Men: First Class and X-Men: Days of Future Past). Standing at 6ft 3inches (190.5cm) I could see him having the same intimidating presence as Ben Affleck's Batman (standing 6ft 4inches). Out of all the Robin's I can see Nicholas as an older Dick Grayson (Nightwing).... Maybe an older Jason Todd as Red Hood?
Plus, it helps a lot that Hoult is a really good actor and a very versatile actor. Also, I wouldn't worry about his weight too much because there are three reasons why I say this! 1.) They (studio, director or producers) will more than likely assign him with a personal trainer or put him in a rigorous boot camp with other actors. 2.) His costume can do most of the work for him.. A lot of these superhero costumes theses actors wear are filled with some sort of extra padding and muscular details on the suit to create an illusion that they're much larger. 3.) Remember this isn't the comic book "universe" meaning it's difficult to translate the godly physique from comics into real life unless you use unnatural substances.
For number 3 I would think of Michael Keaton as Batman... Not necessarily a very physically intimidating actor, but he made up for it in his acting abilities. Like actor Manu Bennet said (paraphrasing) "It's all in the eyes, you can express countless emotions with one stare."
I'll say it right now Jesse Williams would be my first choice to play Tim Drake aka Red Robin (or Dick Grayson). I've been keeping track of Jesse Williams acting résumé and majority of the time he plays a very strong/intelligent leader. I think his best character is Jackson Avery from the hit medical drama television series, Grey's Anatomy (I had to watch it with my family when I was younger so don't judge!).
BOO-HOO! Cry me a river if you're feeling some type of way about this choice, but I see a lot of potential with this actor. I don't see Taylor Lautner as a great nor terrible actor.. After his success in Twilight his acting career has been dry, but I actually think he has a lot of talent to become a successful action star!
This scene reminds me of a young, stubborn Jason Todd training with Bruce Wayne-
I'm giving Lautner the benefit of the doubt, a chance to prove himself because he has a big action/thriller coming up this year. What I'm most excited about this movie is that we get to see the young actor show off his athletic skills and watch him kick ass. Hey, at least the dude does most of his own stunts.
Who would make the best Robin?
You may or may not like my 3 choices, but let's be more open minded and creative with our fancasting... I'm just saying!