Depends on where you are going???
Northern Europe I would go June- Sept
The Med or Greece I would go April to early June or Sept Oct Nov
I find Europe is much more historical & more on architecture in nature compared to the Caribbean which is more about sun sand & water sports.
Alexandr Pushkin, Carnival-Holiday, HAL-(old)Westerdam, Orient lines-Marco Polo, Royal Olympic-Olympic, NCL-Dream, Dawn-Princess, ACCL-Grande Caribe, Oceania-Insignia (3), Regatta(4) Marina (1) St Lawrence Cruise Lines-Canadian Empress
Scenic River cruise June 11,2012