They're both fan favorites.

Oh damn.... That is actually pretty hard

Told you it was going to be a good question.

Sure is. It's also harder than diamonds

Neither cause the writers don't hate the characters they write for.
If they hated the cmc they would make sure that the cmc never won a place in the Euestria games.
If they hated spike they would not make him seem like a hero in the Equestria games at the end.
They write in good moments for these characters like being a major role the saving of the Crystal Empire or the cmc winning the position in the equestria games. If they hated them they would write these events differently.

Neither. How would you explain the awesome accomplishments they made? They wouldn't have happened if the writers hated them.

My theory: The writers made it seem as if they're hated so that the episodes where they're seen in a positive light have more impact

The characters do not seem hate the cmc either or twilight would never give the cmc lessons in twilight time or trust the cmc with the book of love spells in the episode hearts and hooves day. And I allready explained spikes end of this.