My favorite is Explorer, mainly because its the only Voyager class I've been on, but would love to try them all. So, far that was are best cruise, lots to do and see just on the ship, very well layed out deck plans, very nice cabins and good food, great entertainment. I also really like the way the pool deck is layed out, didn't have any major difficulties finding lounge chairs like sometimes happens on other ship.
We have been on all 3, with 2 sailings on Explorer. It's hard to choose, because all 3 have distinct qualities. I was most impressed with Voyager, since it was the first of its kind. Explorer and Adventure built on the success of Voyager, corrected some design issues, and were enhanced with their own qualities, such as the oceanographic labs on Explorer.
With that said, I'll have to vote for Adventure, because I prefer the Southern Caribbean itinerary of Aruba & Curacao.
Happy Sailing, whichever one you choose. You can't go wrong with any one!
I would be very happy to sail on Voyager and Adventure to add to my Explorer experience and to render my totally objective judgment. Anyone willing to finance this vital research project can respond. <G>