Split (Croatia) to Venice. What's the best way?

If you must go to Venice, then you can check if you can fly to Milan.
Croatia Airlines flies to Milan Malpensa (MXP), while EasyJet flies to Milan-Linate, however both are seasonal flights, so they probably operate only from May to October, therefore it depends on when you travel.

Flying to Milan will be faster than flying to Rome as the train journey from Milano Centrale to Venezia Santa Lucia is only a little over 2 hours, while from Rome Termini to Venice it's 4 hours (plus the train ride from the airport to Rome Termini), so from the time you land to the time you arrive in Venice 6 hours is the minimum.

If you are willing to take a flight with a layover, then there are more options directly to Venice Marco Polo airport.

Thanks Roberto, we've looked at the Milan option, but unfortunately it's not direct for the day we're flying, otherwise that would've been ideal. Rome seems to be our best option at the moment, given the arrival times of the stop-over flights into Venice from Split, and we're trying to keep our travel days as stress free as possible, hence the overnight in Rome before going to Venice. Appreciate your time in responding :).

Don't know how long you are in Croatia or if there is any flexibility for that part of your trip.

We stay our last night in Rovinj, Croatia and then take a 2 hour catamaran to Venice in the morning.

An interesting way of doing this would be to take an overnight ferry to Ancona. (See it as a mini cruise) and then just a train from there.

Thanks bnelson210, that's an option we hadn't considered and will investigate. Appreciate your time in responding :).

We once took a ferry from Split to Rijeka, then a bus to Trieste and stayed overnight there. The next day was an easy, short (2 hours?) train ride to Venice.

We got to see some beautiful places but it took some time, so is probably not practical if your time is limited.

I’d probably avoid routing through Rome if you’ll already be there for 7 nights later. I’d check the Croatia to Venice ferry options first (here), because depending on your date it can be the simplest way to keep moving north.. If the timings don’t work from Split itself, then bus/ferry up the coast to Dubrovnik, Zadar or Istria and onward from there could still be nicer than flying south. Otherwise, your Rome overnight plan is fine, just not the most logical route.