Uhm, it would be nice to know if you are hooking up active or passive speakers. Speakon isn’t balanced, so unsuitable for hooking up active speakers (although they are the best choice for passive speakers, provided your speakers (and amp) have speakon connectors).
If you are using active speakers and using them outside, I have a slight preference for combi-cable, which has both power and (always use balanced) signal cable in one. Saves a lot of hassle, I can tell you.
As for length, I used to have 10m cables, but considering you lose at least 2m going down from the speaker to the ground, you’ll need some length getting to your mixer. Add a bit of wiggle room to lay the cable so it’s not a trip wire and suddenly 10m isn’t all that far anymore (unless you want to keep your speakers relatively close-by).
15m or 20m are my current cable lengths. I’ve found that it is easier to coil a few meters extra somewhere than it is to start extending cables.
In Europe ProCab has a very extensive collection of quality cables (three quality levels actually) at reasonable prices.
Greetinx,
Chuck