Lead ropes for horses have to be strong, with the right kinds of clips that stand up to a lot of activity. I’ve bought some inferior ones in the past until I learned what to look for when buying them. The clip should be sturdy but small enough to clip to the horse’s halter and easy to release. You do not want to be fumbling with it while training the horse.
If you are buying a rope for a child be sure to get one with a light, small clip. They can’t really handle the larger clips either. So, my recommendation is small clips. It is also important to buy the right material. Soft cotton is better in my opinion on the hands than poly any day.
Another thing to consider is the length of the lead rope. You might need to buy a couple of different ones before you find a length you like. How you intent to use the rope will also factor in the decision.