What are the best extensions to use for vertex and pixel shading (NVidia)

Out of curiosity, I know I’m a few months away from reaching that level, what is the best extension to use for vertex shading and for pixel shading (NVidia card). I understand there are a few available from a few manufacturers?
Also, can one use for instance the NV vertex or pixel shading extensions (assume there are such ones) on any NVidia cards? Or are there different versions for different cards, with some cards not supporting any?
As always, huge thanks for the help,

If your target cards can handle the ARB extensions, then choose them before vendor specific extensions, or you often end up with making more code paths than really needed. if you have a fixed HW you can use nv_* extensions since those often exposes more funcitonallity than the standarlisized once.