More help please, Rome to Venice or vice versa

If you possibly can, certainly fly into Venice and out of Rome (or the other way around). Most of the time, I've found "open jaw" tickets to be no more expensive than round-trip in and out of the same city. Please save yourself the 5 hours of travel upon arrival. Mid-day of your arrival, you could be sipping a spritz at a canal-side cafe watching gondolas slide by on the sparkling water .... or you could be sitting in a train, exhausted. And yes, 4 nights in Venice and 6 or 7 in Rome (giving yourself a day or two to day trip to Orvieto or Naples, or...) sounds like a great plan!

If possible, save the half day it would take you to return to your first location by booking multicity tickets. A flight into Venice and out of Rome makes the most sense, since early flights FROM Venice back to North America are often in the morning, and transportation to the airport can be problematic.

Just to make sure you know, an open-jaw or multi-city ticket is NOT two separate one-way tickets, which can be very expensive, but rather booked on the same ticket, just with different departure points. I think starting in Venice eases you better into Italy, because Rome requires a lot of stamina and it's huge, whereas Venice is small and walkable and a good place to get over jet lag. I adore Rome but I want to be 100% functional when I'm there.

Your better option is to fly into Venice and home from Rome. Rome has many direct flights back to the US. Venice does not. If you return from Venice it generally means a 5am run to the airport to catch a connecting flight to somewhere else in Europe for your return flight to the US. An open-jaw will save lots of time and money. Four in Venice balance in Rome is a good balance. You might consider a day trip from Rome to break it up a bit. However, Rome can keep you very busy. Nearly all of our flights are open-jaw. And do check for two one-way tickets -- you might be surprised.

we did the train from Rome to Venice. It only took 3.5 hours from station to station. (visit the tren Italia website) The station goes right into Venice, so you don't have to deal with the airport bus or taxi. (if you have to take the airport bus or taxi from the airport, you will be dropped off at Piazzale Roma ,which is a short walk to the train station (so essentially you arrive at the same location that the train gets you.) Also, Rome's Termini Station is in central Rome, so you don't have to hassle with finding transport to the airport which is in the outskirts of the city.
If you fly, you have to add the time and the cost to get from Central Rome to the airport, (1hr?) checking your bags, getting through security, etc. Most airlines suggest to be there about 2 hours before departure, so add 2 hours to the flight time, so you are looking to add 3 hours to your travel time by plane, Then at Venice, you must add the time it takes to the airport bus or water taxi to get from the airport to central Venice (add 1 hour?)
So 3.5 hours for the train or 4 hours plus the flight time to fly. Only you can decide whether the hassle is worth it. IMHO, the time comparison is a wash.
For me, from Rome to Venice, I would choose the train.

Thanks everyone, I think the collective vote is as I suspected, fly into Venice and stay a few days, then take the train to Rome and after our stay, fly home from there. Derek, sorry for the confusion - I wouldn't fly from Venice to Rome when the train is much easier.

Thanks again, Lynn