I did about five trips with Nekton which apparently wasn’t enough. The crew and staff were always great, the food usually good but with the downturn in the economy the boats got behind with the repairs. The Pilot had gone in to the shipyard when the other boat had major problems in Mayaguana and there was no back-up to continue the cruise and Nekton had to cancel upcoming trips.
Explorer has some liveaboards in interesting places. Truth offers short liveaboards to California’s Channel Islands but that is cold diving. Nautilus does the west coast from Canada to Baja.
Aggressor has some beautiful boats in great places but is pricy.
I have never forgiven Peter Huges and company for the way they handled the Belize incedent and will never step onto a Dancer boat.
My favorite liveaboard is the Nai’a in Fiji, no other boat or crew has ever even come close to the service they do but a week in Fiji isn’t cheap either.
There are other small liveaboards in the Pacific but all are going to cost you both for the ship and the air to get there.