If you're into horses, you've probably seen these yacht rope leads around. The Knotty Girlz make these right here in the USA, and they're pretty popular with trainers worldwide. They come in your choice of 12ft or 14ft lengths in this nice beige color.
What makes these special is the double braid polyester construction - it's super strong, has great abrasion resistance, and doesn't stretch much. The sunlight resistance means it won't break down if you leave it out in the elements occasionally.
They've got an eye-spliced loop on one end and a back splice with a popper on the other. Makes it really easy to work with your horse, whether you're training, leading, or just doing groundwork. The rope is soft but durable, so it's comfortable for both you and your horse.
I like that it's easy to wash too - just toss it in when it gets dirty from arena work or pasture time. It's one of those simple but well-made tools that just works. Perfect for natural horsemanship approaches.
The Knotty Girlz seem to know their stuff - they manufacture specifically for trainers, so they've thought through what actually works in real training situations rather than just making something that looks good.