We were in Italy last summer - had 6 nights in a villa near Sorrento, so did Vesuvius, Pompeii, Herculaneum, Solfatara, and then 5 nights in Rome - we omitted the Forum as dh and I were bored rigid there before we had dc, but did the Pantheon, Colosseum, Vatican.
Our dc were 9,11,13, had all had "the Romans" as a school topic, they loved it. In between days were the beach, hanging out at the pool by our villa, eating ice-cream, and Rome Zoo.
We were there in July, it was pretty hot. I'd choose Easter if I had to do it again.
Personally, a cruise sounds like hell to me - stuck on a boat you can't get off until they say so? Not for me at all. But I'd totally recommend Italy!