Choosing a speaker cable should be a relatively straight forward process, but its worth keeping in mind any future requirements, especially if the system is for mobile use. Generally it is best to keep speaker cables as short as possible, this reduces losses and keeps loudspeaker damping at its best. You can always consider extending leads using joining adaptors. This is very easy with Speakon & Speaker connectors, since there are plenty of good adaptors available. There also the option to have several lead lengths in you kit to take care of all eventualities.
It is worth noting that the connectors call “Speaker” shown in this section are directly compatible the the Neutrik brand “Speakon”. Most modern equipment use one of these types, but guitar amplifiers often still use ¼” Jacks, so there are plenty of options for this style of lead also.