Rather is usually used in comparison statements. I'd rather have a cat than a dog. I would rather go barefoot than wear shoes. Prefer can be used in comparison statements (if you include the word "over" in the sentence), but usually just states a preference, with no comparison. Using prefer in a comparison statement (with "over"): I prefer chicken over fish. I prefer sunshine over rain. Also, prefer can be used in comparison statements if "as opposed to" is added in the sentence. Using prefer in a sentence (with "as opposed to" added): I prefer sunshine as opposed to rain. (This usage is not common, but acceptable.) *In the US spoken English, "rather" statements are used more commonly for comparisons. Common usage of prefer(no comparisons): I prefer chocolate ice cream. I prefer low impact exercises. I hope this was helpful. :)

I'm not a native speaker, someone will correct me. Rather is an adverb, prefer is a verb. I would rather go to a bar than go to the movies. -> Prefiero ir a un bar en vez de ir al cine. Do you prefer apples or oranges? -> ¿Prefieres manzanas o naranjas? To mean prefer you have to add "would" to rather. "Would rather" and "prefer" can be used interchangeably. Would rather + infinitive Prefer + -ing form