What Mac should i get?

I am looking for either a 27 inch iMac or a 15 inch MBP. I will be using it for final cut pro, final draft, Microsoft office, and like 20 GB of iTunes space. Also, what excessories are recommended for someone who wants to edit, produce and direct? What external hard drive would you recommend? PS- I am not looking for a PC, so don't even try.