Lemanensis wrote:I believe רכב is like vehicle in English, i.e. a generic term.
While true, in ordinary speech it is often used to specifically mean "a car".
I've only heard אוטו in films - it may be common as it's shorter.
I'll also add אוטו has no plural form. If it is indeed more common in certain contexts than the other two, it is only when a single car is discussed.
But as מכונית has the real Hebrew root, rather than an import...
The root m-ch-n is actually imported (from which foreign word should be clear), but I suppose you could say it is hebrew now, and the word itself fits Hebrew noun patterns, unlike אוטו.
I don't really have much to add beyond speculations about the contexts where one word is more likely to be used than the other, which I've however resolved myself to no longer do.
The bottom line is מכונית will never be wrong.