While either will do, I have a slight preference to rope. Soft rope doesn't usually leave burns, and I think there's something romantic or artistic about rope when compared to cuffs. Also, you don't need to keep track of a key with rope, which is nice. It's harder to cut cuffs off someone if something goes wrong. Rope is also versitle. However, for certain times cuffs are a good way to go. Cop role playing works better with cuffs, for example.