Hand Groupings

[Shandrax]

Hello,
I am totally confused about the value of Hand Groupings in No Limit Hold'Em.

Now we all (hopefully) know the groupings from 2+2 "Hold'Em for Advanced Players", but there have been arguments floating around the net that they might have to be adjusted slightly and that they are (or maybe not?!?!?) only valid for limit games.

I have also found someone advocating a counting-system, but I think it can be dismissed easily, because it overrates the value of hands like K9 and underrates the value of 56s for example.

The big problem occurs when you watch the video from Howard Lederer about No Limit games, because he is suggesting groupings that are quite different from what I believed to be the "ultimate truth".

Now my questions are:
A. Are hand groupings a matter of "taste" and experience or is there a mathematically proven ranking that stands once and forever? I mean, is AKs better than JJ or not? Those are the kind of problems I am talking about.

B. Is there a difference in rankings between Low-Limit, Pot-Limit and No-Limit games?

Any suggestions or any links to articles about the subject maybe?