The writing style which is most natural for you is bound to echo the speech you heard when a child. English was Conrad’s third language, and much that seems piquant in his use of English was no doubt colored by his first language, which was Polish. And lucky indeed is the writer who has grown up in Ireland, for the English spoken there is so amusing and musical. I myself grew up in Indianapolis, where common speech sounds like a band saw cutting galvanized tin, and employs a vocabulary as unornamental as a monkey wrench.
In some of the more remote hollows of Appalachia, children still grow up hearing songs and locutions of Elizabethan times. Yes, and many Americans grow up hearing a language other than English, or an English dialect a majority of Americans cannot understand.
All these varieties of speech are beautiful, just as the varieties of butterflies are beautiful. No matter what your first language, you should treasure it all your life. If it happens to not be standard English, and if it shows itself when your write standard English, the result is usually delightful, like a very pretty girl with one eye that is green and one that is blue.
I myself find that I trust my own writing most, and others seem to trust it most, too, when I sound most like a person from Indianapolis, which is what I am. What alternatives do I have? The one most vehemently recommended by teachers has no doubt been pressed on you, as well: to write like cultivated Englishmen of a century or more ago.