The basic difference is . . . whatever the publisher wants. U.S. publishers are not all stuck on Courier.
My advice to anyone about formatting is -- use whatever font is comfortable for YOU to READ on screen, and change it to suit the needs and wants of agents and publishers at submission time. Nothing else matters. The only advantage of Courier is that it gives a good rough page count -- that is what makes it a standard. Times New Eyestrain is the Micro$ith default, intended for printed business letters.