Degrees of comparison

Question

I believe, both variants are possible:

• friendlier / more friendly; and
• the friendliest / the most friendly.

I'd like to know what is used in every day speech more often and which is more formal.

Answer 1

Though grammatically both friendlier and more friendly are correct. But formally since friendly is a 2- syllable word, more friendly is more acceptable.

However, if we go by figures, Google's survey for published works can help you. https://books.google.com/ngrams/graph?content=friendlier%2Cmore+friendly&year_start=1800&year_end=2008&corpus=6&smoothing=3&share=&direct_url=t1%3B%2Cfriendlier%3B%2Cc0%3B.t1%3B%2Cmore%20friendly%3B%2Cc0

According to this survey, friendlier has become more popular after mid-80s

Answer 2

Those whom grew up speaking or around one of the romantic languages like Spanish will often use the [most] and [more], which are superalative and comparative adverbs, because they don't have the comparative, superlative morphemes: [mas bonita] is [more pretty].

I recently spoke to some linguistics students who said that at a conference, someone presented a paper that claims the superlative/comparative morphemes [-est] and [-er] are becoming less common in language in certain regions in comparison to their adverbial cousins [more] and [most] with the exception of most adjectives that are single syllable and don't end with a vowel, words like [tall] or [nice].

I must note that the adverbial words usually get attached to adjectives that are three or more syllables.