You mean coils and leaves? That just depends. There are a lot of things that can be said for both. Leaves tend to provide more stability since they generally have a higher spring rate. However coils ride better because leaves have a built in friction device with the leaves rubbing together. Generally speaking, if you are looking at lots of flex, coils will provide that better than leaves since leaves have inherent limits on how much they can flex. However if you have a long enough leaf spring, then they will match the coils for flex and give more stability.