Hi
I visited Sicily with JY on 5 October 2011. The itinerary at that time was a bit inconsiderate but JY have changed it since then and so it probably runs more smoothly. Lovely part of the world and even in October it was very hot, with less crowds than in the height of summer. Going up Mt Etna was extremely cold though AND snowing! If you like history and architecture this is for you.
So, best time to go is entirely up to you....
Regards
Sylvia