More than anything, it depends on who you are training. In JS, training doesn't depend on height so you can train anyone as long as they are young enough. So if you are training centers or PFs in JS, then it is better to train JS for forwards as it is easier to train and possibly win matches. Also training forwards gives some training in IS through cross-training. But if you are training guards then obviously it is better to train guards. For SF, it's really your choice, and doesn't make much of a difference to your game. I personally would train forwards if I'm training an SF as there would be some training in IS also.
Also never do team training. It's not worth an entire week.