I definitely like to run mixed freight trains with a variety of car types, rather than unit trains. I vary the consist so i'm not always running the same group of cars together. I strive not to mix cars from different eras in the same train.
When i run passenger cars, sometimes i run a matched set, but i also like to mix them up, as though it's an excursion train made up of privately owned cars. (gives me a good excuse to buy individual passenger cars that appeal to me).
