When it comes to chicken and turkey, dark meat is a bit higher in calorie and fat than white meat, but not tremendously (about 30 calories difference per 1/2 cup for chicken). They all count in my exchange plan as 1 meat exchange per ounce, so I buy whatever is is cheapest or best for the meal I'm planning.
I like cooking with thigh meat instead of breasts in dishes that tend to dry out the breast meat. Dark meat is a lot more forgiving when it comes to overcooking, - and it's a whole lot cheaper.
If there's a sale on boneless breasts, I will buy them (I like white meat for making chicken salad) and if there's a sale on bonless thighs I will really stock up.
I even make buffalo, barbecue and asian grilled or broiled "wings" out of bone-in thighs. I cut each thing in half, cutting parallel to the bone (one piece will have a bone, and the other will be a boneless strip) then I marinate in hot sauce, barbecue sauce, or an asian sauce, and then bake or broil them until they're done. So good, and even using the dark meat, they're much lower in fat and calories than wings ounce for ounce - and even more so if you remove the skin from the thighs before cooking.