The port in Venice for the Millennium is the Stazione Maritima. If you have a map and find where this, you will see that it would be tough to find a place that would actually be between both the port and the airport. We cruised Millennium Barcelona to Venice on May 11 and stayed in Venice about a 45 minute walk from the ship- and a half hour walk to St. Mark's Square near the Accademia bridge. We loved the location and the hotel. (It's the Pensione Accademia if you are interested)
If you head over to Cruise Critic and pose this same question of their ports board under Europe, you'll get a lot of responses to your question from recent and this summers cruisers.
We had an awesome time! Have a great cruise- we LOVE Venice!