For breadboards, use thin, single-stranded copper wire. It bends and holds into various shapes and can easily pierce into the breadboard holes. However, for prototyping with copper strip boards such as Veroboards, stiff, single-stranded wire is not ideal. Instead, use thin, multi-stranded wire because it bends around stuff easily and does not get in the way. Also should be very easy to solder once you tin the tip of the wire. Be sure to twist the end of the wire when you strip it.