Not sure I understand your question. Every class is dedicated to a certain attribute. For example potions is dedicated to knowledge. So for each star you reach in that class, you get a certain amount of points added to that attribute (how much depends on if its 1h, 3h or 8h).

Now, for every star, you also get "rewards" that may or may not be points of any kind of attribute. Those should be random. So there shouldn't be a way to tell that for potions you would get more or less, say, empathy than in any other (non-empathy focussed) class.

So there is no "single best class". If you want to grind all attibutes as equal as possible, select one class of every type of attribute and round robin through them. 8h classes should get you the most dedicated attribute points and by having 5 stars also the most chances for random attribute points.