I usually do like 3-4 days per city, so 2 weeks I could easily handle maybe 3 base cities. Like you could do the northern loop with like Venice for a few days, Florence for a few days (and Florence is great for day trips to Bologna or Pisa or anywhere there), and then maybe either Rome (where you could do Pompei on a day trip if you want), or maybe do like Cinque Terre or Como if you want something a bit quieter. Or you do the central section which is more like Rome and Naples as bases, and probably adding in Sorrento and Capri along the way.
Whatever you do, you want to make sure you have a chance to go by some of the smaller towns like Sienna or Lucca or a million others. They've got a charm to them that you definitely will miss if you stick to the "name" cities.