In my novel Praxton, Slaves of the Rogue World, the female characters all wear collars and usually cuffs. I used cuffs in the novel for several reasons.
The first is that cuffs are always on and makes it easy for her Guardian to quickly join them together or attach them to chains. The cuffs and collars on Praxton were also considered part of the fashion accessories. They often matched and could be of an elaborate design. Females did not leave their bedroom without a collar on and often choose cuffs to go with outfit they were planning to wear that day.
I also choose cuffs over ropes for one other very good reason. Females on Praxton were expected to take very good care of themselves and spent a good portion of each morning preparing themselves. That effort would be partially defeated if ropes were used and left marks on the skin. On Praxton it was illegal for the Guardian to leave permanent marks on the female skin.
There is nothing wrong with ropes; certainly to the female they may make her feel even more restrained as they put pressure on area where they are attached. Ropes can also do more than just secure limbs. They can used in breast bondage and make the breast and nipples more prominent. In addition they can circle the waist and go between her legs to make crotch rope. These all allow the male to control her very effectively and help stimulate her as well.
The preference is always personal and can be a combination of the two. For beginners cuffs may be better. Ropes can be put on too tight and there is a small risk of pinching her skin if not done with care. Not sure which to use on her? Ask her and then restrain away!