Katniss

Agreed with the posts above. As much as I like Isabelle, she was simply too young to play Katniss. She may have matched the physical description perfectly, but Katniss essentially carried the movie as the protagonist and therefore required an actress who could display the emotional and psychological maturity, range, and toughness (while also showing vulnerability). Few lines of dialogue almost meant that the majority of emotion had to be conveyed though facial expressions and in a nuanced way. Isabelle had demonstrated her extraordinary potential in Orphan as a child artist and was critically acclaimed for her performance but, at the time, Jennifer was also a rising star (especially with the success of Winter's Bone) despite being 7 years older than Isabelle. In fact, Katniss was Jennifer's breakout role and her launch pad to starting a serious adult career, after which she went on to be Oscar nominated in Silver Linings and has been one of the most highly paid and sought after actresses in the industry ever since. Sure it was a difficult call to make, as is any casting decision on such a big budget production as the Hunger Games, but I think they played their cards well and it paid off. Not to take anything away from Isabelle of course, as she is a promising young talent herself and will have a very bright future if she continues to make great/interesting choices.