That's a trick question, of course, because it depends on the purpose for which the English is being used. A professor, for instance will speak very differently when teaching from a mother with a one-year-old child.
(Mind you, part of this difference will be caused by the fact that the mother will be trying to make it easy for her student to understand.)
Despite this, there are some sorts of English which have long been held up as an example to us all. Formerly it was Received Pronunciation, or RP, which was basically the style of speech affected by a slightly pompous highly educated person of a previous generation.
More recently, people have talked of something called BBC English, but beware, because I recently came across this utter monstrosity on the BBC Sport website. It was previewing a soccer match that took place on Saturday 30th March 2019.
Millwall's nine Championship wins this season have all been achieved having had fewer possession than their opponents - Leeds have had more possession in 37 of their 38 league matches this season.
Personally, I don't know whether to laugh or cry.
Yes: poor old Millwall lost.
Word Not To Use Today Unless You Know What You're Doing: fewer. The irony is that football commentators are often mocked for using less instead of fewer. Now, however, I realise that things could be much much worse.
The word fewer means not as many and less means not as much. It's not even as if it's difficult.
The Old English form of fewer was fēawa. It comes from the same ancient root as the Greek word pauros, which means small.