There are many approaches to the game – Fewer but longer trainlines (Distance adds to the price of the deliveries) for slower but larger payouts. Or you can make a higher number of lines with a more stable but lower payday (Like coachwagons in every city in a region)
The key thing is not to starve your industry and keep trains from short routes. A city will only accept as many goods as the industrial buildings in it can accept. Any more and the industry will turn down production (and acceptance of raw goods), turning your lines into a money hole.
While the slow moving trains might seem like a great alternative to a wagontrain line early on, their speed will quickly reach a point where they can pick up goods faster than the industry can make new ones, resulting in trains that do nothing but cost you a lot of money in maintenance.