Any of these Sicilian towns better as a base for a few nights?

I think Ragusa would be a good base for the Baroque towns.

I visited all four in 2015, and it seemed Ragusa needed more time than the others, so that would be my preference as a base. Ragusa is a bi-level city, so definitely research the parking situation around any potential lodgings.

Note: I depend on public transportation and thus tend to prefer larger places with better transit links. With a car, your situation is different.

All four towns have rail service, though it's fairly infrequent. Ragusa, Modica and Scicli are close enough that you might be able to day-trip between them by train if you wanted a break from driving.

Siracusa is where I would base myself. Driving or taking a direct train from Siracusa to:
Ragusa (1h 30m) by car / direct train (2h 15m).
Modica (1h 45m) direct train / Scicli (1h 30m) direct train / Modica to Scicli takes 15-minutes by direct train.
Noto (45-minutes) direct train.
Villa Romana del Casale (2h) by car / Piazza Armerina (2h) by car / Villa Romana del Casale to Piazza Armerina takes 15-minutes.
Mt Etna (1h 45m) by car / Rifugio Sapienza (1h 45m) by car / Mt Etna to Rifugio Sapienza takes 15-minutes. Randazzo (1h 45m) by car / Linguaglossa (2h) by car / Randazzo to Linguaglossa takes 30-minutes.

We stayed at Terra Dei Limoni, a bed and breakfast in a lemon grove about 7 km from Noto, near the coast. It was very pleasant and peaceful. Was a great base fir day trips into Noto and Ragusa.

On our 1st visit to Sicily it followed a tour of Southern Italy. Our tour ended in Taormina. On our own we based ourselves in Ortigia for five nights and visited the baroque towns of Noto, Ragusa & Modica. We had planned to return to Sicily in 2020 and spend a month. Due to the lockdown we had to cancel. Our plan was to return to Ortigia & stay 4 nights in the same B&B. We had a large apartment on the top floor with a sea view. Great place, wonderful host & perfect location for sites & restaurants.
https://www.laviadellagiudecca.it/
Edited to add: Our planned itinerary for 2020> https://community.ricksteves.com/travel-forum/trip-reports/my-trip-to-sicily-in-zoe-s-memory/

These are fantastic ideas...just what I hoped for...we will check out all of them! (It is great to leave the car behind at times and do the train for a break...) Many thanks, Susan

I visited all of these towns this summer, including Siracusa that several people have recommended. I also rented a car and drove everywhere. If you want to stay more in the Ragusa area as you originally mentioned, then Ragusa is the best place to stay. There's a lot more to see and do there, and parking is very easy at the free parking lot next to the Giardino Ibleo. The drive up is pretty steep, but there are always free places to park and I stayed in an AirBnB a few blocks away, so it wasn't a problem.

If you decide to make Siracusa your home base and drive to the other towns, I would strongly advise that you find a hotel/apartment relatively near the Parcheggio Molo San'Antonio Siracusa, or at least within walking distance across the bridges in Ortigia. The AirBnB I booked in Ortigia said they had a parking spot right in front of the apartment. Driving in Ortigia was the worst experience of my entire Sicily trip. I won't recount the entire story, but I ended up parking at the lot I mentioned above and just walking. So much less stress. The parking lot on the mainland was 15 Euros/day and there was a guy at a little stand selling tickets, which seemed rather sketchy, but I checked later and it was the same price as from the parking machines.