Over the years, I've tried a lot of different speakers cables ranging from the original Monster Cable to $6K MIT cables and many in between. As others have stated, there are no absolutes and a cable that works well in one system won't necessarily be optimal, or even decent, in a different system.
However, more often than not, I've found that a braided copper cable of the kind popularized by Ray Kimber of Kimber Kable has performed well on a broad range of systems. Kimber 4TC, 8TC, and 12TC is available bulk from a number of vendors, so the long cable length you are looking for can be constructed without much difficulty.
This geometry provides very low series inductance, fairly low capacitance, and the combined parallel cables provides low resistance.
This same type of basic cable construction (without Kimber's latest Varistrand conductor geometry) is also available at a significantly lower cost from Asian suppliers. I can't say if this bulk cable is as good as Kimber's (since I haven't owned these latest models), but I have built some speaker cables using this bulk cable that sounds very good. If you search on ebay for 12TC OCC speaker cable, you will find it available for approximately $20/meter.
I would absolutely not buy anything branded Kimber from a Chinese supplier, since more than likely this is someone trying to rip off Kimber's trademark. But any intellectual property rights Kimber may have once had on the basic braided counter-opposed helix geometry has long since expired.
The bulk cable is hollow inside the braids (as is Kimber's basic version). I used a wire snake to pull a 1/4" cotton rope through the middle of the cable. This helps dampen vibration and keeps the cable geometry consistent. Terminating with good quality connectors results in a very nice sounding cable for a modest investment.
