Visiting the world's highest volcano has to be on a bucket list of everyone! Etna is also the world's most active volcano listed in the UNESCO World Heritage Sites. Spring and late summer would be a good time to take a stroll around Mount Etna, since the weather is the most appropriate and you might also see amazing wild flowers.
June and July are quite crowded, and winter is rather cold. On the other hand, if you go sometime in January you will witness the snow capped mountains and can do some skiing in the Sapienza Refuge ski area from which you can reach the crater at 2920 m! No matter which option you prefer, the best experience would be to see the spectacular lava-producing eruption! Unfortunately, these are difficult to predict.