Well it has to be Italy doesn't it?
Think of the size of that country and the contrasts from North to South. Every city I've been to was great though, so you can't go wrong no matter where you go.
Rome at Easter will be heaving - Il Papa and the Vatican ceremonies etc. and I suppose most big cities will be the same, but without the religious significance.
Anyway North - Torino, Milan (half a day, then go to Lake Como?) Verona, Padua, Venice, Bologna, Florence, Lucca,
Of the above my favourites were Bologna, Lucca, and Padua. Padua is a gem, just 1/2 hour from Venice on the train, so the best of both worlds.
Then further South, Rome of course, Naples, Sorrento, (Pompeii and Herculaneum) Positano, Capri etc. My favourite was Salerno, a little less polished and chi chi than Positano and Sorrento, but great and a super view from back in the hills and train direct to Naples and connections to Pompeii
That's enough to get on with, now make a choice!