Italy in March - Venice, Cirque Terre or Lake Como?

I vote Venice.

Trying to add 2 places is contra-indicated. Just one more.

I'll second the vote for Venice. It seems a good fit for you, as it is very picturesque and romantic. In March it should not be too overly crowded. Because the weather in March could be pretty wintry, I would not choose either Lake Como or Cinque Terre.

Given the very short time frame, you might consider limiting your trip to Venice, Florence and Milan, with day trips if desired. Keep in mind that each change of location will require at least half a day (and sometimes more) when all is considered, so you won't really have eight days for touring.

One possible way you could structure the trip......

• arrive Milan / MXP, take train to Venice straight away - Venice, 2 nights.
• train to Florence, 4 nights - while there you could take a day trip by bus to Siena or by train to Lucca or the Cinque Terre.
• train to Milan, 1 or 2 nights if you want to take a day trip Varenna on Lago di Como.

As previously mentioned, the Cinque Terre may not be the best choice at that time of year due to the weather, but also because it doesn't "officially" open for the tourist season until the beginning of April. Not all hotels and other facilities may be open in March.

If you haven't travelled in Italy before, there are some potentially expensive caveats to be aware of when using trains and other public transit. If you need more information, post another note here.

In order to plan the most efficient sightseeing, I would highly recommend packing along a copy of the RS Italy guidebook. That has an enormous amount of information on the sights in each city, operating hours and how to get reservations to avoid queues (although queues might not be much of a problem in March).