How should chicken breasts for a chicken salad be cooked?
It really depends on the texture you are looking for in your finished product. If you want a chunky chicken salad then bake your chicken breasts seasoned or not, I season mine, and then cube them. If you want something a little more exciting pan grill the breasts to the point of a little char and then dice. If you want your chicken to be flavorless and get all of your flavor from the mix you are tossing your chicken into, boil it or put it in a slow cooker if you are cooking up a big batch. 

It all really comes down to how you like to eat your chicken salad, and more importantly how pretty you want it to look in your serving method, because a cajun blackened chicken salad sandwich can look down right homely. I say try them all until you fall in love with one temporarily and when that has lost its passion try a different version. 

Also as a side note if I am preparing it for me and not for someone else, so it doesn't have to be all white and pretty, I use thighs instead of breasts since they are more forgiving and generally cheaper. If I am not just breaking down a whole chicken and using the leftovers.