First of all Rebounding - It should be on a high level for stronger leagues as most of the rebounds gets C/PF positions and if your opponent's center has better rebound etc skill he might get a good amount of Offensive Rebounds which usually leads to second points. Secondly ID + Shot Blocking - For real I'm more into ID than SB, but it's a fact the higher level these two defensive skills are the better results C will give to you. And last thing - Inside shot - This is not most important thing for Center, of course the higher the better so he could score in that second chance situations or in some plays BUT as person mentioned before passing-jp-jr skills not very important in my opinion in C position - as It's will be hard to train center with normal height these skills (mostly waste of time) if you want all around center - just use universal PF or Even SF as they will usually has REB,ID,SB skills as well.