That is a question that is impossible to answer without having a ton in information. For instance, what size is the plane? How much experience do you have building? What is your level of expertise in flying? Will the aircraft be throttled? But the simple answer is if you are limited to only two control surfaces, it would be rudder and elevator. Now tell us what it its you are attempting to do and there will be many folks who will be willing to enter into a discussion. Your question, is it is, is simply too vague to answer.