If you're into hiking or scenery, go with Cinque Terre. If you like ancient ruins, go to Naples (nearby sights of Pompeii, Herculanaeum, Paestum near Salerno). As for Sorrento, I'd actually base myself out of there for the above ancient sights rather than Naples. Naples is a big, noisy city that is somewhat intimidating to folks. Sorrento is smaller, quieter, and more accessible.
Of course, my opinions only...
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"Life is not measured in the number of breaths we take, but by the places that take our breath away..."