For best results with airflow through the case, which does a lot for temperature control, especially with the cpu/gpu, you'll need intake-in and exhaust out. How you go about that isn't nearly as important as actually doing it. As mentioned, if you have a aio, it's radiator is usually mounted as exhaust, so that fan counts. If you have air cooling, you'll really want a fan exhausting that heat out of the case,nkt letting it circulate. Just taking one of those intake fans and putting it in the rear/top will drop case temps an easy 10°C, which has a corresponding affect on the cpu and the gpu.
Personally, I'd get 2x decent fans at least. This'll provide enough airflow through the case to actually allow the fan rpm to be turned down, making the case much quieter, while still getting good temps.