For me, physical and mental must be equal to quality for all outfield players. Middle row, ML, MC and MR are equally balanced, AM slightly towards attack, DM slightly towards defence, ST even more towards attack, DC even more towards defence, but DL/DR will be treated like DM because they will help me attack sometimes. GK is a tough one, but I usually put everything towards defence, and a bit to physical and mental.

If a player plays in two roles, for example ML/AML, then I will make him a bit offensive.

Of course, the above is my optimal distribution, but sometimes I get an MC much more tilted towards attack/defence than I'd like, and I spend the season trying to bring him to my optimum and sometimes don't reach it.