Both get good reviews, though the Caribbean Explorer is, at the moment, the Caribbean Explorer II, which, up until January was Peter Hughes' Sea Dancer in Providenciales. The original Caribbean Explorer is now in refit getting ready to begin life anew in Providenciales. I was on Sea Dancer (noe Caribbean Explorer II)three years ago and it was a nice enough boat -- not the best liveaboard ever but the price was right (Oh crap -- you said not to mention price -- sorry!), though I stayed in the "twin" cabin, which was very small. The meal and common area is enclosed only by heavy vinyl sheets but was air conditioned when we wanted it to be. I won't comment on the crew because it is obviously different now that the boat is somewhere else. The diving and sights around Saba /St. Kitts might be a bit more exciting than what the Nekton has to offer but it will be deeper diving. The Nekton (from all reports) is a much larger boat and stable boat with larger cabins. Never been on it, though. I was in Curacao a couple years ago as well. I stayed at Habit Curacao and thought it was very nice. At that time, the Habitat house reef made diving off the resort pier quite pleasant. Can't comment on its current condition, though. The boat dives out of Habitat were nice, if a bit farther than the boat dives out of the resort I stayed in on Bonaire. I made the mistake of going into Willemstad on Curacao -- apart from the slave museum and the oldest synagogue in the Western Hemisphere (really!) it was a typical cruise ship town (ugh). Dove in Bonaire several months ago and enjoyed that as well. Much more flexibility if you're land-based. I guess it all depends on what you want. Your wife is a diver, I trust . . .
Mike
PS Really, those are the only two liveaboards available? Sometimes if you call Peter Hughes' booking office, they have short lead time deals, as does Aggressor
PPS Please, nobody flame me for saying the words "Peter" and "Hughes" in the same sentence -- I am aware of what happened two years ago (I was in Curacao then and saw it all on CNN).