Pete C. wrote:
Like everyone else said, stranded for flexibility pulling through
conduit and whatnot. For termination at receptacles and the like, get
the back wire type devices, not to be confused with the push wire type
which suck. The back wire have a hole you stick the wire in and then
tighten the screw which clamps the wire solidly. This is similar to
terminals in plugs and works well with stranded wire.

Very good advice.