I actually use a combination of stranded and solid wire.
I use solid wire for my feeders. It is easier, or at least it seems easier to me, to solder a solid wire to the rails than it is to solder a stranded wire to the rails.
But under the layout my bus wire is stranded. I use only 14 awg wire for my rail bus. This is possible because of the positioning of my command station in relationship and my add on boosters. The maximum length of rail bus wiring from the command station or the add on boosters to the extreme end of the wire bus run is no more than 15’.
I am in my third DCC layout since 1994 and I have not had any problems with the method I use. I have measured the voltage at the extreme end of each rail bus leg and I have not had more than a .25 voltage drop which is minimal in my opinion.
I wired the 30” x 62” traveling layout my model railroad club uses. I used 22 awg solid wire for the feeders and 18 awg stranded for the rail bus. The rail bus length from the command station to its farthest point is no more than 90 inches. Upon close examination of the voltage at various points on the traveling layout I noted, using a RRampMeter from DCC Specialties, only 0 to .1 voltage drop anywhere on the rails.
What to use depends on many factors. Cost is almost always a factory. Heat/Cold and humidity can play a factor. Size and type of the wire to be used plays a factor. Then again so do the skills necessary to connect feeders to rails and feeders to rail bus.
There is no absolute right answer on the type of wire to be used other than the wire gauge. Wire gauge always is affected by resistance. The larger the wire the lower the resistance. The longer a wire run also is affected by resistance. Even the number of feeders can affect a trains overall operations. Let us not forget that soldering skills also plays a part in wiring a layout.
Model Railroader in both N and HO since June 1965
Digitrax DCC user since October 1994