Phantom Boats. Mostly because they were always breaking.
Canal Boats of the World was a close second, though. Nothing to see!
As much as we all, myself included, deride some of the modern day failures, they don't hold a candle to the ones which flopped in the early days. Innoventions is huge, has massive capacity, is air-conditioned, offers probably thousands of hours of variable entertainment if you were to play every video game type they offered. Contrast that with an unthemed cruise around the shrubless lagoon, with a one in four chance that your boat would break and they'd have to go get you.