Is "most favorite" a valid combination?

Solution 1:

Language and logic do not always go hand in hand. Most favorite and least favorite are both commonly used by native speakers. The way favorite and unique are used by people who have better things to do than worry about the minutiae of grammar is closer to a hyperbole than a logical statement about something. Just because people say something is their favorite doesn’t necessarily mean it is literally their favorite.

However, you should always err on the side of caution and avoid expressions that may be controversial to some people. I wouldn’t necessarily recommend using most favorite in a formal context.

When in doubt, rephrase it.

Instead of saying:

Recess and lunch were my favorite subjects, but lunch was my most favorite.

You can simply say:

Recess and lunch were my preferred subjects, but lunch was my favorite.

Solution 2:

No

Don't use 'most favorite' in your own speech.

This used to be fine.

Favorite is literally a Romance variant of 'favored' or 'favored one'. It should be able to describe comparative levels of favor and used to do so. The OED lists a cite for 'favoritest', presumably for the word's two-syllable pronunciation, but 'most favorite' was always more common. Like the ngram shows, that usage fell off a cliff in the 19th century.

It isn't now...

Thing is, English already had plenty of words for 'favored' and 'enjoyable', so this word became used for the particular sense of 'sb or sth liked more than all others of the same kind' and thus for 'most or best liked'. That's the general sense now and saying something is the 'most most' or 'bestest liked' is going to annoy the same group of people that dislike 'uniquer' and 'most especially'; it's much worse than 'winningest'.

That is not to say some native speakers won't still say it—it's the same kind of inclusive or hyperbolic superlative that shows up in things like 'best best friend' and 'best BFF'. Thing is, those native speakers are mostly going to be younger, less educated, and often female. There are volumes that are written on this—the best gloss shows up around p. 53 of D.F. Wallace's Harper's article on SNOOTs and the Usage Wars in his spiel to gifted students of color in U.S. higher education—but Standard Written English looks down on that dialect. It's not right or fair; it's still a fact of professional life for many people in many English-speaking places. Unless you're intentionally aiming for coming across less educated or puerile, you should avoid taking Mr Lloyd's inclusiveness at face value.

...with some very limited exceptions.

There is a set contrast between 'most favorite' and 'least favorite', where the later doesn't mean 'lowest ranked among favorites' but 'most disliked', at least out of the available choices (all of which might otherwise be fine). This is a pat comparison and 'favoriter' and 'more favorite' are now essentially unused.

The question was write from dictation. I know I should write whatever I heard. But I think they should still make sure the sentences have correct grammar.

Having said all of that, the answer to this question is

Maybe

because this very much depends on the instructions you've received from your teacher. Subtitles or transcripts should read essentially verbatim, with only—and optionally—the removal of minor verbal tics like filler words such as 'um', 'uh', and 'er' or removal of dialectical pronunciations such as writing 'I am fixing to' when the speaker actually said something like 'Imma fixin' teh'. Otherwise, you should preserve the speakers' word choices, even when those reflect a nonstandard dialect. On the other hand, a doctor or lawyer may expect their secretary to emend their dictation to Standard Written English before passing it on to the court, client, or patient. Which one your class is training you for—and grading you by—is very much something to ask your teacher about.