Kenneth G. Wilson (1923). The Columbia Guide to Standard American English. 1993.
favorite (adj.)
In My favorite dessert, favorite is an absolute adjective; no modifier can be added, so My most favorite dessert is Nonstandard, an objectionable hyperbole. In A favorite dessert, however, favorite can take a modifier, as in a very favorite dessert, one among many favorites, perhaps. See ABSOLUTE ADJECTIVES.