RivaTuner will give you more options and flexibility when overclocking your GPU.
It will also give you the option of saving your OC profile and applying it at startup.
They both have the same basic function but I would prefer RivaTuner.
i have the nvidia control panel also and it doesnt auto load custom settings, even if you create a profile rule to load at windows start up. mine has never worked i always had to manually load it by going into the cp. so get rivatuner, it does auto load your custom settings at windows start up and its easier. also get gpu-z so you can see your gpu info fast.