The order does not matter. You can install them all at the same time even. However, I do recommend that if you do nvidia first, and it pulls down xorg-server as a dependency, that you at some point use the -D option to mark it as explicit.
This will tell you which driver to use:
http://www.nvidia.com/Download/index.aspx?lang=en-us
You might also consider xf86-video-nouveau.
Check out the "nvidia" article on the Arch wiki for some good info.
