What is the best (cost effective )order to travel Western Europe?
We are going to Rome, Venice, Paris, Nice, Barcelona, Ibiza, and London. We are planning on taking the train and flying when the prices are comparable. What is the best order to go to all of these places if we are starting in Rome? Which are the best ways (train vs flight vs bus) keep in mind we are 2 girls in our twenties.
Thanks 
Start in London and work your way down.
London–Paris–Barcelona–(ferry/flight to) Ibiza–back to Barcelona (if by ferry)–(or flight to) Nice– and from there you can either go to Venice then Rome, or Rome then Venice, but it would probably be cheaper to fly out of Rome to go home. Either way the train trips are fairly long (9hrs to Rome is the shortest trip, 8hrs shortest travel time to Venice). There don’t seem to be any night trains on either route so you may want to look into a flight between Nice and Venice and then train down to Rome and fly home from there.