My preference is the Western Caribbean. I have taken both. I wasn't terribly impressed with the Eastern but it was enjoyable. I am taking the Western again in January because I enjoy Grand Cayman especially. The entire Caribbean area is a distant second to Alaska however!
Western Caribbeam Carnival 2005
Eastern Caribbean Holland America 2006
Alaska Diamond Princess 2007
Western Caribbean NCL Jewel 2008
Southern Caribbean Holland America Westerdam 2008