It depends on how you use them. If you are going to be struggling a lot or have them on for a long time, it's more than just the pain (and yeah, metal cuffs DO hurt more than neoprene etc) Nerves and blood flow can be cut off if you aren't careful with metal, and a little fluffy cover on metal cuffs might not help all that much.
I much prefer either leather or neoprene cuffs, as they hold more securely, rarely leave marks and if used properly, should not cut off circulation or nerve flow.
If ANY form of bondage results in tingling or numbness, it's time to call Safe Word before permanent damage is done. Pain is one thing, permanent damage is an entirely different story.
Well made leather, neoprene or leather substitute cuffs can be used without pressure points occurring, which is really the best idea. IMO, metal cuffs are mostly for show, videos and photo shoots, not real long term B&D situations.