Safety Tether

[Brion Toss]

As the above responses indicate, there are a lot of options for lifeline tethers, so many that I believe we have bumped the original question: webbing vs. 3-strand. As I understand it, webbing is the dominant material for this application because it folds flat so easily, and doesn't stiffen or hockle. Rope is handy, by contrast, when you have to run over a sheave. Different tools for different jobs. If I were going to use rope for a tether, I'd use the most flexy type --- single-braid --- and Brummel it at the ring ( a Ring Hitch is too bulky, too snag-prone). And I'd make it 2-legged, to lengths I prefer; I don't want someone messing with my gear.
As for length, the shorter the better. I have read too many reports of people drowning at the end of long tethers, which just happened to be long enough for them to fall over the lifelines and into the water. High enough lifelines and somewhat shorter tethers will help, and Ian seems to have something like that, but even with falling overboard prevented, I want the shortest possible potential fetch-up at any moment, which for me means chest-high jacklines. It also happens to mean material preferably stronger than 6,000lbs, which is a scant minimum in a shock load, particularly with wear factored in.
As for the awkwardness of clipping and unclipping, I certainly understand the attraction of a free run fore-and-aft; I just see the midship interruption as an entirely acceptable bother at worst, so of like seatbelts, and a distinct feature in fact, as it limits how far you can wash along the deck. And chest-high jacklines make great lifelines on their own, highest just where you are most vulnerable to going over: in the middle of the boat. I sometimes rig and use them even if I am not wearing a harness.
Fair leads,
Brion Toss