Either will be my main machine. Switching from an XP so it will likely be a brave new world for me. I have an iPhone and iPad to tool around on. Since I have only ever worked at my desk I foresee 99% of my future work to be done there as well. However, it would be very nice to be able to work while on vacation or at my boys sports events rather than just tooling around on the iPhone/iPad. I LOVE the idea of a 27inch of the iMac. Hard to give that up for only a 15 inch Macbook. Currently I already have a 1 terabit external drive. So the extra storage is a non issue. Do you have either? Which do you prefer?