Because the noun car is modified by the superlative adjective best, and because this makes the noun car definite in this context, we use the Which of them is correct It is best not to do something
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Here, we have the adjective best, but this adjective is attached to no noun.
In the following sentence, however, best is an adjective
What was best? if we insert the word the, we get a noun phrase, the best You could certainly declare that after comparing a number of things, you found that a particular one of those things was the best That is to say, it was better than any of the others. So, it is the best ever means it's the best of all time, up to the present
it was the best ever means either it was the best up to that point in time, and a better one may have happened since then, or it includes up to the present. Which one is the best is obviously a question format, so it makes sense that which one the best is should be the correct form This is very good instinct, and you could even argue that the grammar is good, but at best it's unnatural. Both sentences could mean the same thing, however i like you best
I like chocolate best, better than anything else can be used when what one is choosing from is not specified i like you the best
Between chocolate, vanilla, and strawberry, i like vanilla the best can be used when choosing from some choices. It's best that he bought it yesterday Or it's good that he bought it yesterday 2a has a quite different meaning, implying that what is being approved of is not that the purchase be made, but that he is the one to make it
3 it's best (if) he (not) buy it tomorrow. is not a subjunctive form, and some options do not work well. 1 your example already shows how to use best as an adverb It is also a superlative, like greatest, or highest, so just as you would use it as an adjective to show that something is the ultimate example of it's kind when used as an adverb you do so to indicate that the adjective it precedes is to the highest degree possible. Either is fine, but (american here) i think something that best suits your needs would be the most common way of saying it.
5 in europe, it is not uncommon to receive emails with the valediction with best/kind regards, instead of the more typical and shorter best/kind regards
This is the best ever song that i've heard This is the best song ever that i've heard
