We have only gone from Europe to the US. Those who have done it the opposite way say by the time they get off the cruise they are exhauted.. We do our touring in Europe and then spend the rest of the days at sea.. We have always been able to sit by the pool and the whirlpool coming back.. What is there to do on the ship..what is there not, ...movies, cultural lectures, wine tasting, art auctions, sales, a library, and whatever else you would like.. I could go on and on.. On the other hand.. I like "contemplating my navel"..lol..just sitting and reading a book. I have always been able to use the balconies on the way back from Europe..delightful..
For me.. I enjoy the fall and early D ecember in Europe (still very warm) and the ships hug the coast where the weather and sea are warm.. We have left from Barcelona three tiimes.. If you do take Ft. Lauderdale to Barcelona.. there is great h otel you might want to stay at and so much to see.. we even have a private english speaking guide.