If most of your work is personal, or for the web, or for certain printing firms, your color mode should be sRGB.
If most of your work is for publication, offset printing, etc., Mode II Adobe RGB is a better mode.
My work is for the latter, so I go with Adobe RGB, As I understand it, this mode uses a very wide color gambit that suits well when transferring image files from RGB to CMYK for printing in magazines, etc.
If your work doesn't need to be converted to CMYK, then sRGB is much better.
I try to keep up with this stuff, but it does change.
