It's difficult to tell. I have a left winger/attacking mid who was an assist machine and he had low defence, high attack, decent physical.

I think it depends on your style. I'm starting to think although attack attributes is important for an attacking mid for example, I think physical stats are very important for high pressing as your main choice but it wouldn't be so important if you play a defensive style, defence stats would be important for your CMs.
Does all that make sense?

To be more clear, for an attacking formation which require a lot of strength fitness etc etc I would train physical + attack for offensive players and physical + defence for defensive players.

If I sway more to a defensive formation then physical and defense would rule over every player but strikers.