中々(なかなか)Very, Quite, Considerably

When used in affirmative sentences, なかなか and かなり both convey the nuance that something exceeds expectations, e.g. なかなか美味しい ('It's quite tasty.') or かなり美味しい (essentially the same meaning). The main difference is that なかなか is often used in negative expressions to suggest that something is not easily done, e.g. なかなかうまくいかない ('It just won't go well.'), while かなり is not used this way.

なかなか means 'quite' or 'fairly' when used with positive expressions, e.g. なかなか面白い映画だった ('It was quite an interesting movie.') In contrast, なかなか～ない expresses difficulty or delay, meaning 'not easily' or 'hardly', e.g. 仕事がなかなか終わらない ('The work just won't end.')

なかなか and あまり～ない both express degree, but in opposite directions. なかなか implies exceeding expectations, e.g. なかなか美味しい ('It's quite tasty.'). In contrast, あまり～ない suggests a lesser degree, or falling short of expectations, e.g. あまり美味しくない ('It's not very tasty.').

Both なかなか and けっこう are adverbs used to express extent. In affirmative sentences, they can both mean 'quite' or 'rather.' A key difference is that なかなか is often used in negative sentences to express difficulty in doing something. Meanwhile, けっこう can be used alone (especially as けっこうです) to politely decline something, like saying 'I'm fine.'

Both express degree, but with different implications. なかなか implies something is quite or unexpectedly good, e.g. なかなかいい店だね ('This place is surprisingly good.') あまり highlights an excessive degree that leads to an unintended or negative result, e.g. 緊張のあまり声が震えた ('I was so nervous my voice shook.')

Both emphasize degree, but differ in nuance. なかなか suggests something is quite or surprisingly so, often with a positive tone, e.g. なかなか面白い映画だった ('It was quite an interesting movie.') あまりに means 'too much' or 'excessively', and is often negative in tone, e.g. あまりに寒くて出かけられなかった ('It was too cold to go out.')

Though both contain なか, their meanings are different. なかなか is often used in negatives to express difficulty, like 'not easily' (なかなかできません), or in positives to mean 'quite' (なかなかいい). In contrast, のなかで means 'among' and is used when referring to one or more members of a group. For example, 果物の中でりんごが一番好き means 'Among fruits, I like apples the best.'.