Let me break the word "toward" down for you. In the American English language, there is no proper way to use the word "towards." Toward is the American word for, "In the direction of." The latter is used in England. Please feel free to use towards whenever you desire, and of course mistakes always happen (I am completely guilty.) However, a flippant refusal to even attempt to speak and write correctly shows a particular race of people something I'd like to let you in on. When I alone (am I not necessarily a member of the aforementioned race) hear people use towards, that are not British, I think, "Man that person does not read much, or does not pay attention to their reading (hence why they need bookmarks.)" And, "Man that person must have no interest in the fact that they sound like an idiot while attempting to sound intelligent."
In America, we add a S to the end of a word for a few reasons. Some of the uses of adding a S to the end of a word are to make the word plural, to make the word possessive, to make the word a conjunction, or to make the word's use suitable for a gay man. It's not a matter of when one sounds better over the other. It's a matter of the fact that Americans speak American English, and a deficit in the ability of Americans understanding their own language reeks of a brain injury suffered from head-on-collision with a semi.
One thing I have also noticed is that good screenwriters sometimes use both in one screenplay. Why is that? Because details matter and towards makes the dumb characters sound more dumb. Meanwhile, to those of you that wish to continually bask in some sort of intellectual discourse about the word, and cling to a misdirected sentiment in which, "It really is a matter of what sounds best to the writer" I say, "Shut up dummy, you don't know what you're talking about."