Well it can't be comparable as both were good in their respective roles.
Both the characterization was totally different. Motivation were different. Fatima rebelling against her father Aamir was not for the same reason Rithika rebels against her coach Madhavan. Right from the basics till conflict point is all different.
Just by shear acting, Rithika was a bit more perfect. Only coz she had to carry the film on her shoulder supporting Maddy right from beginning whereas Fatima comes to picture half way through the film. This is where actress playing her younger version dominates.