First of all, thank you very much for taking the time to reply.
Sometimes I find certain japanese constructions a bit awkward because they defy spanish(which is my first language) and,sometimes, english grammar structures. Anyway let me take this opportunity to ask a second question:
If クラスの中で一番たくさん食べるのは誰ですか is the most accurate way of asking "who is the one that eats the most in the class?", what would クラスの中で誰が一番たくさん食べますか actually translate to? "in the class, who is the one that eats the most?"?