Correct spelling, explanation: preferred can be either an adjective or a past participle of a verb prefer. Preferred is formed under the rule that the verb that ends with a vowel and a consonant and has an accent on the last syllable has to have the last consonant doubled and added the suffix ed. This spelling is applied both in the case of an adjective and a verb. Therefore, the correct version is preferred and not prefered, where one r is omitted.

Definition of preferred:
adjective: favourite, liked, or wanted more than something else;
An elegant dress would be a preferred option for this party.
verb: past participle from prefer;
– to choose, like, or want something more than something other;
She always preferred a simple glass of wine rather than fancy cocktails.
– to accuse someone officially;
My attorney advised me not to prefer charges against my boss, because there is not enough evidence.

Incorrect spelling, explanation: prefered is the incorrect spelling of a word preferred. Preferred can act as an adjective or a past participle from a verb prefer. Prefer is a verb ending with a vowel and a consonant with an accent on the last syllable, so before adding a suffix -ed the last consonant has to be doubled. This spelling rule applies to an adjective and a verb. For that reason prefered is not correct, because there is one letter missing. The right spelling is preferred.

Incorrect spelling

Incorrect spelling