I think working on both is good. What works best for me is anxiety reduction by "meditation"(just sitting alone quietly for ten minutes a day and focusing on breathing slowly and relaxing) this always helps me return to my normal level of stuttering when k notice I've been worse than usual lately. And exposure therapy but not avoiding situation I don't like. I make myself go through the drive through occasionally and I maks myself talk on the phone all the time, just so when I don't have a choice I know I can do it.