When I brought Wilson home, he only picked at his food for about a week or so. It really took him time to settle in, and chow down--now he eats like a champ (he's been here a little over 2 months now). I do think some dogs just need some time. Don't leave the food down, feed him at scheduled times and then pick the food up.
Whatever food you choose, I would give him time--don't assume it is the food he doesn't like, until you are sure he has acclimated to your home.