We are passing through Sicily traveling by ferry from Naples to Palermo, then the ferry from Pozzallo to Valletta (Malta). With a few days in Sicily, and wanting to visit Mt. Etna, can someone suggest 4-5 day trip? Should we stick to only the east side (Palermo, Cefalu, Taomina, Syracuse) then Pozzallo or should we try to include a trip to the west side to visit Agrigento? Also, while a ferry to Malta seems like fun, another option is to skip the ferry and fly from Catania to Valletta? Is Agrigento still having water issues and discouraging tourists?
Palermo and Cefalù are in the north coast and Agrigento is on the south coast. If Mt. Etna is a must, then stick to the east coast; Taormina and Syracusa.
To me, seeing more than a couple cities, is unrealistic with the time you have.
There are a lot of sights in and around Palermo. I'm not sure how much time you'll have left after you consider your options there.
I considered hopping over to Malta after I spent 17-18 days (not long enough) in Sicily back in 2015, but I didn't like the ferry situation. It departs from an obscure town you wouldn't otherwise visit, and I though the cost was very high for such a short trip. Perhaps the cost situation, at least, has changed. But I would recommend checking the flight options on skyscanner.com.
If you are coming into Palermo and also want to see Mount Etna, with only 4-5 days I would keep it very simple- 1-2 days in Palermo, then get the train to either Taormina or Catania and spend 2-3 days there, from where you can visit Mount Etna and then fly to Valletta.
I'd spend more time in Palermo than in Taormina/Catania, but I guess that's because I'm more of an urban sightseer than a nature/scenery person. Also, Taormina is crammed with tourists when there's a cruise ship in port at Messina. I could only stand it for 2 or 3 hours. I'm not the only one who had that reaction, but there are definitely people who love Taormina, so YMMV.
You're already taking the ferry from Naples to Palermo. That's a nice crossing; especially as an overnight as it replaces a hotel + a day of travel. There's no good reason to do a second ferry from Pozzallo; a port that's on the exact opposite side of the island and really isn't much of a destination in its own right.
Palermo & surrounding area is an absolute gem IMO and well worth 4-5 nights. The thing is... you really don't have much time in Sicily so a transit all the way across to the east side of the island to see Etna seems to me like a poor use of your very limited time.
Alternatively you could skip Palermo, fly from the Italian mainland to Catania, spend time there and visiting Etna and then take the train down to the Pozzallo. (or fly to Malta)
Another off-the-board option is to spend a couple of 2-3 nights in Catania/Etna and 2-3 nights in the Baroque hill towns. Renting a car isn't a bad idea of you do this. Drop the car in Pozzallo.
I don't think Agrigento works particularly well with any of this. You're just adding another poorly connected destination in a short visit.