The quad ski is the coolest one. Love transforming cars and all, but it seems like the best blend of both a water vehicle and land vehicle. The characteristics of each just mesh better in a single rider vehicle. With an amphibious car you just have a car that can float, it’s not a boat, but with the quad ski it’s like you have a jet ski and an 4 wheeler.They're all good. The efficiency of each vehicle will entirely depends as to where, how, what are going to use it for. Each of them have their own purpose. Kudos to these inventions.