The 4s has more mid range torque which is great for blasting out of curves. Also better suspension. Some of the 4ss were fitted with a very good ABS. Later (post '03) had better seat and more protective fairing.
I suggest you search for either and settle on the best bike for the money. Insist on complete service records. Even if a dealer didn't do all the work the right owner will have kept receipts for oil, etc. If you go with a 4s demand all keys including the red key.
Jeff in Colorado