Okay so I've been told two things. One, that upgrading crew is more important and two, that buying tutors is more important. So which one is it!?!?!
Upgrading is pretty much the basis of this game. You want to become the strongest. But tutors are important, because they are going to give you that extra cash in battles. When you upgrade, you want to make sure you have enough left over to keep some tutors around.