The 568ex II and 560ex can slave CLS from the popup flash, but the models without the "ex" suffix will not.
RF wireless is more reliable but for a small area, 15meters or less in light-protected areas and very short range in sun. If one is using flash triggering only occasional optical triggering is fine. But if you are using remote flash a lot or in events or weddings get the 622tx /622n RF controllers which are good for 3-10 times the distance, rock solid in trigger reliability and avoids the need for line of sight for the optical control flash signal.
RF wireless is more reliable but for a small area, 15meters or less in light-protected areas and very short range in sun. If one is using flash triggering only occasional optical triggering is fine. But if you are using remote flash a lot or in events or weddings get the 622tx /622n RF controllers which are good for 3-10 times the distance, rock solid in trigger reliability and avoids the need for line of sight for the optical control flash signal.