We will be in Sicily in mid-september and will have only a half day to explore one of the medieval hill towns. Which would you recommend -- Noto, Modica or Ragusa?
Caveat: I have not been yet, but will be going to all three in September and did a lot of research and reading on them.
Where are you coming from to reach any of the towns (Siracusa)? If time is really tight, maybe consider minimizing your travel time to get there so you could at least see one of them more fully. Look at sites/attractions in each one and perhaps pick based on that. I'm most looking forward to Ragusa Ibla, but that's mostly because I really want to photograph it and I want to try their famous cheese. They are somewhat similar (all baroque) but Ragusa Ibla looks a little more colorful, for lack of better terms.
By the way, Trip Advisor has a lot of threads on Siciliy and these baroque towns, so look there as well if you don't get many comments.
I haven't been to Modica yet, but it's pretty much a toss up between Noto and Ragusa. Noto was mostly rebuilt after a devastating earthquake, Ragusa has two parts - you probably want Ragusa Ibla. Ragusa was a little more interesting.
We stopped briefly in Noto for lunch and stayed in Modica that night and part of the next day in 2012. Modica wound up being one of the highlights of the trip, and if/when we return to Sicily, returning to Modica will be a priority - highly recommended. It has two parts, too, the high and low towns. Be prepared for getting around by stairs between the two.
In the Modica lower town, be sure to visit the exquisite chocolate shop Antica Dolceria Bonajuto.