24AWG vs 26AWG for mechanic reliability
Both those sizes are rather small (and probably have to be) so it would be better if you can support them in some way or use a multicore cable. For example, we avoid individual conductors smaller than AWG20 in aircraft. See, for example, FAA publication AC 43.13-1B


  a. Mechanical Strength of Wires. If it is
  desirable to use wire sizes smaller than #20,
  particular attention should be given to the mechanical
  strength and installation handling of
  these wires, e.g., vibration, flexing, and termination.
  Wire containing less than 19 strands
  must not be used. Consideration should be
  given to the use of high-strength alloy conductors
  in small gauge wires to increase mechanical
  strength. As a general practice, wires
  smaller than size #20 should be provided with
  additional clamps and be grouped with at least
  three other wires. They should also have additional
  support at terminations, such as connector
  grommets, strain relief clamps, shrinkable
  sleeving, or telescoping bushings. They
  should not be used in applications where they
  will be subjected to excessive vibration, repeated
  bending, or frequent disconnection
  from screw termination.


Chances are for a hobbyist who will only use it for short run times, you would be fine with ordinary stranded 105°C PVC insulation AWG24 wire. If the wires get flexed continuously during operation you may wish to go for a higher number of strands, thicker insulation. We use a very expensive PTFE/Polyimide insulation system, but I don't think you need that unless you're building military drones. 

The terminations may be of more consequence than the wire itself- failures tend to happen near the terminations if the wire can bend sharply and repeatedly near (say) a crimped or soldered connection then it will tend to fail there. Always try to keep the wire strain relieved and constrained so it can't flop around or bend back and forth unnecessarily and does not have to bend sharply unnecessarily.