I cant agree more use the right one for the Job - I am also in the same situation working on both and Loving both for different reasosn

Regarding the Video support issue, I know first hand installing an ATI card is pretty hassel free (works out of the box) and you can use the normal SystemSettings tools to setup a dual screen quite easy.
As for nVidia it also quite easy asof a 2 years or so ago - they have standard install packages for the drivers and appy which makes it as simple as installing on Windows