I really like Palermo and it’s one of my favourite Italian cities and there’s plenty to see in the city. Catania is ok and it’s more walkable and compact but there’s less to do in the city. As with all large towns and cities in the south and Sicily, they’re chaotic and not the cleanest.
If you’re looking for things to do in the surrounding area and not just in the city, Catania is probably the better of the two and you can also go up Etna, which is fantastic. There are excellent transport links (cheap, regular buses) from Catania airport and the main city station across the whole island.
I expect to see Palermo back in Serie A within the next few seasons.