The Greeneway (417) is usually the easiest route to use, even if it costs around $4 in cash. It is much quicker to get on from Sanford Airport and, while it is a bit longer, it is rare to get any hold-ups, and it takes you right to Disney's door at Exit 6 (for Epcot, Downtown Disney and Magic Kingdom resorts) or Exit 3 (for Animal Kingdom resorts). You certainly CAN do the journey quicker going via Lake Mary Boulevard and I-4, but, with most British charters arriving from 3-6pm, you would be hitting I-4 downtown during the evening rush hour, which can be pretty ugly and add at least half an hour to your journey time.