What do you think the most important skill in English is? why?

The speak is the main important as the writing. Reading, Spelling, phonetics and vocabulary improve your conversation.

Vocabulary of course because with50 words you can say very little but with50000 words you can express various ideas.

Mastered speak it as well as writing, both American and British

There are4 skills in English: namely Listening, Communicating, Reading and Writing.For me all of these are very important because if i say that communicating is the most important  among the English skills, one should be good in pronunciation, grammar and know a lot of vocabularies.Reading and writing also are very significant when dealing with other people.

Speaking  and writing are the most important ones simply because they are productive ones; they give feedback about the level of the learner

The4 skills (reading, writing, listening and speaking) are categorized as receptive (Reading and Listening) and Productive (Speaking and Writing). Receptive skills are more important as the more you receive the better you produce. Specially reading is important as it teaches you the sentence structure, use of grammar etc.  

I would say getting the basics right is the most important skill that has to be achieved because expressing deficiencies in it will bring you greater embarrassments and you would eventually refrain from communicating in English which is a sign of demotivation. 

Therefore getting the basics right is the most significant skill while trying to master a language. Building your Vocabulary is secondary and no doubt that will take you to greater heights. 

All of them are equally important - speaking, writing, reading listening, phonetics, accent

 In my opinion listening is the most important skill .It's the beginning of learning any language .From listening the mind stores vocabulary ,then all the steps follow .

 , if you mean one skill ...I prefer the writing skill because it is the best way to acquire the other skills ...