I prefer to buy the chicken breasts, remove the skin and cut out the bone/cartilage, and then pound them with my meat tenderizer.
Cheaper and just as good a product.
Chicken thigh is dark meat, which means more fat. Fat IS flavor, and helps keep things tender. But chicken breast is healthier for you, and pounding it makes it as tender as thigh meat.
It depends on what your attitude is about food .. how much you eat for fun vs. how much you eat for health. You CAN have both, you know.
But cutlets (whether bought that way or made that way at home) are always a better choice than the whole breast. Cutlets will be a consistent thickness throughout, so you get even cooking .. .rather than some areas over-cooked and dry, and other areas not cooked enough and perhaps a potential source of food poisoning ... and sometimes we have to overcook the outside when cooking a breast.