Question about ND filters.

[dvboy]

Just wondering about getting the exposure correct using ND filters.As an example on a semi bright day my ND16 is over exposed using the 2:1 ratio of SHUTTER/FPS (60/30) and my ND32 is under exposed,but closer.Using my ND32 should I increase the shutter speed altering the 2:1 ratio to get proper exposure,or would it be better to keep the 2:1 ratio (under exposed) and brighten it up in post processing??Thanks and hopefully I explained myself clearly!!

 

[dvboy]

I guess a third option would be to increase the ISO,but I assume that's something to be avoided.