The main advantages of Fastrack are the ability to easily assemble and disassemble layouts and the built-in roadbed. Much better for temporary layouts and carpeting, as mentioned. A bit less likely to develop continuity problems in some people's hands. It's also better looking to some.
One of the main advantages to me is you are much less likely to slice open a finger assembling and disassembling Fastrack than tubular track. I use work gloves when I work with tubular for this reason. Fastrack is more expensive, and can be noisier. But the safety issues when dealing with children in particular, and the ease of assembly and disassembly have me sold, despite the cost.
Also of interest is the availability of command control ready switches, which minimize wiring and facilitate walk around remote control with Fastrack.
