It depends on what video card you have. If you have a 2MB S3 Virge DX or something like that, you might want to stick with 16 bit color because you might be waiting for a second or two for the screen ...
While there's definitely a visible difference between 16 and 32 bit color, i doubt that there will ever be consumer level cards with 64 bit color. 24 bits is enough to produce more colors than the ...