Our shortest was 6 days (Caribbean, including Key West) and the longest was 21 days (Panama Canal-New York to San Francisco), with most being 7 days. (we've cruised about 25 times). 6 days is too short and 21 was a bit too long. Right now we prefer 7 as we have been sailing Mexico or the Caribbean. But if you go 'all the way' to Europe (from the States), I think the 12-14 day cruises are best. The crossings (we sailed Europe then from Iceland to New York among other crossings) are certainly worth the trip, but those 5 days at sea are long, in those waters.