Concept:
Different wiring systems require different levels of skill, safety, cost, and installation time.
Step 1: Cleat wiring is simple and temporary.
Step 2: Batten wiring and casing-capping wiring are also comparatively easier to install.
Step 3: Conduit wiring involves laying wires inside metal or PVC conduits.
Step 4: It requires proper bending, cutting, threading, fixing, and pulling of wires through conduits.
Step 5: Therefore, conduit wiring requires highly skilled labor.
Hence:
\[
\boxed{\text{Conduit wiring}}
\]