What are the factors for the best flat could be? regarding an apartment in a neighborhood like Maadi, Which is the best location?

 it depends, on what makes you comfortable. Some people like sunny flat while other doesn't like them. Furthermore, you will find that people like a flat with a good view. And we usually find good views on higher floors. In addition, Terrace or garden spaces can play a big role when choosing your flat. on the other hand some people like quiet places other like noisy places or full of life areas.