Flash development tool

Hey all,
i am thinking about using a flash development software and i am wandering what is the difference between these three:

  1. Flex
  2. FDT
  3. Flash Devloper

I know that flash developer only works in pc but i heard it has some better features over fdt. (i use both mac and pc but prefer mac) All i know about flex is that it is for Rich application development. I also looked up the prices on these and they are expensive. Do you developers buy these or download from bit torrent?

Thanks, in advance