1) To say one tactic is better than the other is incorrect. The effectivesness of tactics depends on a multitude of factors, from your own team set up to your opponents skillset to even the tactic your opponent is using. As such, we can't tell you which tactic is more effective for you to use. You will need to experiment to see which tactic your team plays best in.
2) Team training (Free Throws, Stamina, Form) trains the entire team in these skills, these are special cases. If you're saying that an individual position like Center only trains faster than 2 positions (PF/C), you are correct. Focusing on one position results in faster training, training 2 positions for that training option trains more players but at a slower rate. Your choice.