My opinion is that the best you can do in this game is to have 5 balanced players.
PG - with good Inside Shot, Rebounding, Inside Def.
SG - with good Inside Shot, Rebounding
SF - with every single skill at a good level (even Shot Blocking)
PF - with good Passing, Handling, Jump Shot, Outside Def.
C - with good Passing, Handling, Jump Shot
Note that all of the players must have good Stamina and Free Throws.
So, in my opinion there's not a most important position but 5 key players that will play well in every tactic.