[3.5 ToB] Swapping Schools

[lsfreak]

Isn't diamond mind the strongest, followed by devoted spirit then iron heart?

There was a thread some months ago about the power of the disciplines. I don't remember for sure, but I think it was something like:
Devoted Spirit
Diamond Mind/White Raven/Tiger Claw
Iron Heart/Setting Sun/Shadow Hand
Desert Wind/Stone Dragon

@OP:
I'd tend to go with what different classes can't take, rather with what they must, and even then I probably wouldn't limit it. Take into consideration the power level of the discipline too - no dropping Desert Wind for Devoted Spirit or White Raven, but you could drop both Stone Dragon and Desert Wind for one of those.