If you have electronic ignition, the type you should use what is recommended by the ignition manufacturer. Pertronix, for example, recommends the type with coil wound center, and advises against solid copper wire. Otherwise solid copper is okay if you do not care about radio interference. If you are going through wire looms or have a helmet type distributor, be sure to get wires 7mm in diameter, not 8 or 9. Do not skimp on quality, or you could have problems starting when it is wet and humid.