Both are good sources of protein, but dark meat is a better source of iron. For calorie and fat content, they stack up like this:
Turkey
3 ounces white meat turkey—133 calories and 2.7 grams of fat
3 ounces dark meat turkey—159 calories and 6.1 grams of fat
Chicken
3 ounces chicken breast—142 calories and 3.1 grams of fat
3 ounces chicken thigh—151 calories and 5 grams of fat