Almalfi Coast and/or Cinque Terre

Not knowing how many days in total your trip is and all your planned destinations, my guess is skipping CT would not result in 'missing' anything.

Given the massive crowds in CT, I'd skip it, and spread that time amongst your other stops.

One would need to evaluate your overall plan and itinerary to give a proper answer to your question. But personally I would not consider the Cinque Terre as a “must go” place if that came to sacrificing more important places like Tuscany. Consider that the Cinque Terre is somewhat out of the way of most typical itineraries and, in part thanks to Rick Steves, too crowded compared to the 1980s when I used to go every year in July.

I was lucky enough to have a short visit to the Cinque Terre in 2008, before it became a huge tourist destination. I spent several days on the Amalfi Coast in February 2 years ago. The quaint CT villages were colorful and very picturesque and I thought a 28 hour visit was just enough for an easy hike and lots of great photos. The AC was the opposite - the villages weren't especially charming or picturesque but the natural beauty was incredibly stunning. I hope to go back some day when the ferries are running - I'm sure the views are even better from the sea.

We have been fortunate enough to have visited both the CT and the Amalfi Coast, both in early May. They each are unique experiences. Our favorite was the Amalfi. We stayed in Salerno and took ferries to the villages. Positano from the water is striking. Our favorite stop was Ravello where we had a one of a kind picture perfect day. On the other hand, we stayed in Monterroso on the CT and faced 2 days of nonstop rain. We toured the villages before the crowds got oppressive, but we just felt something was lacking. I have no idea what your experience would be in Sept. but given how compact the CT villages are and how overcrowding can affect all aspects (trains, streets,restaurants), I would pick the Amalfi.

JR, the Amalfi Coast is not undiscovered, although Sept may be less jammed than our late May visit. Be sure to allow for travel time in and out if the AC, especially your departure day. Multiple means of transport are needed, and they don’t run late after dinner.