I prefer long mixed trains both real life and model. I find these trains more appealing from a standpoint of interest. Visitors seem to have fun seeing what kind of car is exiting from the tunnel next!
I do run unit coal trains at times up to 18 cars including some gondolas with coal loads. These trains are usually pulled by a N&W Y6b ( MTH ) at very slow speed with lots of smoke pouring out of the stack. Sometime I double head a 0-8-0 & and a 2 - 8 - 0 ( Lionels ) instead of the Y6b on unit coal trains. At other times I may use a B&O consist of SW 9, RF 16 Sharknose, and a GP9. Other times I use my Canton end cab switcher with a calf unit or two running at very slow speeds.
I also run long unit box car trains ( 15 - 20 cars ) pulled by a Reading or Virginian Trainmaster,or J Class 4-8-4, or Baldwin Demonstrator RF 16 Diesels in AA lashup, or two scale sized GG1s.
Todays running was made up of three mixed freights. One longer train was comprised of two depressed center flat cars with transformer loads, several gondolas with junk loads, tank cars, hopper cars with coal loads, and a single box car. Pulled by a Canton end cab switcher and SW 9 calf.
Todays second trains was comprised of box cars, covered hoppers, tanks, open hoppers with coal loads, an empty flat car, with caboose. Pulled by a Reading Trainmaster
The third mixed freight ( running on the Mountain Division ) was a short train of one flat car of logs, and a tank car, with caboose, pulled by a SW 1 ( Ma & Pa ) All three of these mixed freights running simultaneously was quite an interesting site to behold.
Fun time in Patburg on the Free State Junction RR.