Of the three main types, front-loading washing machines are actually the slowest. Top-load washing machines are the fastest, followed by top-loading high-efficiency machines. Front-loading washing machines, however, generally get clothes cleaner.
Front-loading washing machines take longer to do a load of laundry because the washer only partially fills with water. As the tub rotates, it repeatedly lifts the clothes out of the water and then drops them back into it. Since the clothes are not completely submerged, it takes longer to get them clean. The time savings with front-loading washing machines comes in the form of reduced drying time due to more effective removal of water during the spin cycle.