Absolutely NO ONE would be better for the role of Grumpy than Peter Dinklage! He's an amazing actor, has played the grumpy dwarfs Trumpkin in The Chronicles of Narnia: Prince Caspian, would definitely draw in a big audience (Which equals MONEY) because of his Game of Thrones fame, is an actual little person, and is so amazing that shows and movies are writing him in roles that weren't meant for a little person just because of how popular he is and how amazingly talented he is. I don't know who I would pick for the other dwarfs (But I do think it should be restricted to only little people) but he would be absolutely PERFECT for Grumpy. No one else would be able to do the role justice but him in my opinion.