Is this a set phrase: "best of all"?

[Dima]

Test No. incompl/elem-15 "An Easy Question", question 1

What exercise do you like doing ......... of all?

(a) next
(b) best
(c) after
(d) before

Test No. incompl/elem-15 "An Easy Question", answer 1

What exercise do you like doing best of all?

Correct answer: (b) best

Your answer was: incorrect
What exercise do you like doing before of all?
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why is best ? I chosen 'before'?

Dima

[Alan]

You cannot say before of all - two prepositions here do not make sense. You need best because this is the superlative form meaning the most favourite.
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English as a Second Language
You can read my ESL story Conditionals

[MadokaLiu]

[Manjula]

why I can not use after all.

[Schwartz]

Can i use 'most of all' instead 'best of all'?

[Kitosdad]

Schwartz, You can in everyday conversation, but that was not included in the list of possible answers.
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Englishman living in Germany.

[Livia Mackie]

My thoughts: The word "like" in this context is not a verb transitive. It is not like X dislike.In this case "..like doing the best of all" means an expression "to like better". If I think about the verb transitive "to like" I would answer "after of all". Because only after to do all exercise I can choose each one I like more than another one. Am I right to thing like (one more like to mess up) that???

Ops! I don't think I was clear in my question, but I hope you can understand it.