I used many types of wire depending on it's intended use.
12 and 14 ga THHN for track power busses with 20 gauge track drops (only inches long).
Several types of HVAC multi-conductor thermostat wire for block detection, signal drivers, and Lighting.
I used 4 pair phone wire for the Tortise swich machine drive and position detection.
Here are some photos.
Control panel wiring
Block detection and signals drivers