All of those are terms of endearment, and the meaning changes depending upon the context. There are people who are just naturally friendly and will address total strangers as "Honey" or "Darlin'" during the course of a conversation. This is just their way of being sociable; there is nothing romantic implied. If two people are involved in a romantic relationship, then words like "Sweetie," "Baby," etc. are much more personal. As far as which word conveys the strongest meaning, there really is no hierarchy.
By the way, while folks might use "Sweetie" or "Darling" in casual conversation without being offensive, "Baby" should never be used in this context. "Baby" can be used between spouses, lovers, boyfriend/girlfriends, siblings, or parents and children. If anyone else uses it, it sounds either demeaning or pathetic.
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