Each of them requires its own paradigms and conventions. Writing good UI code that works cross-client (especially on mobile) is often a challenge that requires

Each of them requires its own paradigms and conventions. Writing good UI code that works cross-client (especially on mobile) is often a challenge that requires different thinking than backend code. On the other hand, backend requires you to think about databases and scalability, which may not be your bread and butter. I genuinely enjoy each of them for different reasons. I don't think it's tenable to argue that one is objectively harder than the other.