It is somewhat dependent upon which tier you are at. In terms of a non legend, I would think that St Andrews and Kiawah are both about even, when you get to legend, they both get much longer and much more difficult.
BPB is fairly difficult but when you move to legend it doesn't become much harder. Since those of us who are Legends or higher rarely get to play the shorter tees anymore sometimes we forget how much easier STA and Kiawah were back 'in the day'. A good example is I think the 13th hole at Kiawah is around 485 to a fairly narrow fairway from the Legend tees, basically a good drive and then around 190 to the pin. From the up tees it is around 390, a drive and a 100 yard wedge.