Italy--Priorities :(

1. Hands down, Siena. It has an incredible Duomo, and the whole town is beautiful. It is in the middle of Tuscany with easy access to other parts of the region. Orvieto is a nice town in Umbria. It is on the train line from Rome and the Autostrada. I think the easy access is why it is visited so much over other towns. If you want to see Umbria, visit Assisi, Spello, Monefalco.
2. Sorrento has easy access to what you list as options and is a pretty town with of Naples and Vesuvius across the bay of Naples.Good dining too. Local train takes you right to Pompeii. But, perhaps you want to stay on AC in Positano to just relax? However, difficult to get to Pompeii from there.

The only question I can answer is #1, and that I can't really answer fairly because I've been to Siena and not to Orvieto.

But I think visiting Siena before you visit Florence will provide a much richer overall experience. Both Siena and Florence were important medieval cities. Then one got frozen in time due to plague, and the other experienced a glorious renaissance. Visiting Siena first, you will then see what might have been in Siena. Like Florence, you will progress from the Middle Ages to the Renaissance.

I'm sure Orvieto is wonderful and has a lot of fans, so I wouldn't vote for Siena over Orvieto. I'm just offering what I think is a particular benefit you will accrue by visiting Siena.

Enjoy your trip. It sounds fabulous!

Siena was our preferred town vs Orvieto. There is do much more to see and do and it oozes charm. While Siena is bigger of the two, it wasn’t that hard to get away from the crowds. We would go back in a heartbeat.

Orvieto was one of my very favorite spots in Italy.
However, in your context, Siena makes much more since.
Have a great trip! Go back again to see the rest.

1) Siena, for reason already mentioned. Orvieto would not be a bad/wrong choice, but to me Siena is the better choice

2) Sorrento easy access to Pompeii and great views-- have stayed here and would happily do so again-- https://ilnido.it/
Check out their webcam--- the real view is even better

3) Not done this tour, but doing the dome climb at St Peters was a highlight

hey jules
how fun and exciting your first trip to italy, you'll love it!
you can check out:
eatingeurope.com for food and wine tours in florence and rome.
oldfrascatiwinetours.com (30 minute train ride from rome) read about us and blog
withlocals.com "beautiful countryside day trip: castelli romani"
enjoy and have fun
aloha

I was surprised by the responses, as I much preferred Oriveto to Sienna. In Oriveto we had a delightful day in the park picnicking, walking and enjoying the views. Siena was just a mass of people the day we were there.

Jules,
I went on the 7 Days in Rome tour and loved it! In my free time, I went to the St. John Laterna Church, I believe the first church that Constantine built. Saw the Church where Michelangelo’s sculpture of Moses, I think, the Church of St. Peter and Paul. I’m writing from memory, I was there in late March 2017. Saw the National Museum, very interesting, near the Termini station. I visited the Capitoline Museum, don’t know if that’s on your tour or not. Walked a lot.
I took a cooking class through Walks of Italy on my first pre-tour day. So much fun! Went to and wandered through the Campo de Fiori area.
If I think of more things, I will write again.
You will love it!
I would vote for Siena over Orvieto if you have to choose. I enjoyed Orvieto very much as well.

1) Orvieto. Siena was interesting but a mass of tourists. (And by that point, I had had enough of churches.) Orvieto was charming, not too crowded, and empty after 5 PM. If you go to Orvieto, I suggest Restaurant Charlie. They specialize in pizza but it was some of the best pizza I have had anywhere.

2) If you are going to Pompeii, then Sorrento should be your base. From Positano and Amalfi you would have to catch the bus to Sorrento first. That could take awhile with traffic. If Pompeii wasn't on your radar, than I would suggest one of the two Amalfi coast towns. I was on the Amalfi coast a couple of weeks ago and traffic was already bad. NInety minutes from Amalfi to Sorrento.

You all don't make it very easy! :) I think I've decided on Sorrento for the Naples/Pompeii/Amalfi area. Sounds convenient and atmospheric. Any recommendation on getting there from Rome? I'm hearing about water taxis from Naples. We could take the train from Rome to Naples or Rome to Sorrento if the water taxi seems expensive/cumbersome/not worth it. Sure wish I'd been to Pompeii before 79AD to enjoy it. ;)

Still debating Ovieto vs Siena. We are going late in October. Will the crowds be any lighter? do they let up much in the evening? We will come back on another trip for the rural areas of Tuscany and Umbria. It looks like transportation wise Siena may be a bit more convenient tho from my reading it could be a bus from Florence to Siena makes more sense than the train for that same stretch.

Judy B., thanks for the ideas for Rome!

Jules,
The reason I vote for Siena is the Cathedral has a floor that is engraved with amazing scenes. It's simply spectacular. Also, I believe I remember a sculpture by Michelangelo there. There is a wonderful library in the cathedral you can go through. Fabulous!
We enjoyed the Campo, great for people watching. Great restaurants too.

I had lunch in a wine bar in Orvieto that was fun and a perfect spot for people watching. Enjoyed the Cathedral there, very beautiful. Also, toured a smail Etruscan Museum across from the Cathedral.

You can't miss whichever city you choose. Just think you will come back again!

Re transportation to Sorrento. The first part of the trip will be a Freccia train from Rome to Napoli Centrale. Then you have to decide between the Circumvesuviana train (local commuter train) or the ferry. I haven't heard of water taxis, but if they exist, I would bet on them being expensive. Since this will be in late October, there will be a higher chance of rainy weather, so I'd play it by ear and decide on the day whether to take the ferry or not. Bear in mind that the town is a long uphill climb from the ferry dock. But taxis should be available.

I've been to both Siena and Orvieto. Both were very nice, so really you can't go wrong either way. Orvieto is a bit smaller and very nice to walk around. There's also Etruscan caves you can visit with a guide, which are very interesting. Siena is gorgeous and Il Campo is just fun to walk around and people watch. Both cities have beautiful duomos.
I agree with staying in Sorrento to go to Pompeii and to relax. We stayed there for 4 nights and it was very nice. About getting there, there were four of us splitting the cost, so we opted to hire a private driver from the Napoli train station straight to our hotel. It was about 120 EURO in 2014 and totally worth it. Enjoy, I'm jealous you have so much time in Italia!

I did the Rome tour some years ago, great intro to the city and the sites. Not included in the tour I was on was a visit to the Ghetto area. Very interesting from many perspectives and also quite moving. I took an excellent food tour of the Testaccio area before the tour began. We visited Ostia and I chose to stay on at the site after the group tour finished and explored it further of my own. A wonderful site and very few visitors. Our hotel was near the Vatican but our guide (Ben) made sure we were supplied with transit passes and knew how to use the Metro and which buses to take to get back from the Centro area. Near Termini, the train station, the Baths of Diocletian and close by is the National Museum of Rome. I don’t think we visited the Trevi fountain as part of this tour so another option to choose. And you may find you want to go back to some sites.