Have been on both Ventura and Arcadia and for us it would have to be Arcadia everytime, unless you like lots (and I mean lots) of children. Arcadia is child free and we did the Venice,Split etc cruise this year on her, WONDERFUL. No children but all age groups on board and after its pending refit will be even better.
Try and choose a cruise with an overnight stop in Venice as only one day cannot do it justice. Will doubt if we will ever sail on Ventura again, like lots of fellow passengers, so there will be quite a few bargains to be had as they try to fil her.
Completely agree with Thurlby of Walsall. Arcadia would be the ship of choice and child free a bonus. Second choice would be Aurora. In Dubrovnik, I would advise you do your own thing and 'walk the walls', you will see everything and it's superb ightseeing at 8 Euros entrance.Go for it and happy cruising.Richard.