I would go with the hobbywing to have more options. 6s would be insanely quick and probably uncontrollable. I started on 2s and just the jump to 3s was highly noticeable. 2s is just slow!! But really i wouldnt just jump to 6s right away. I would start at 3s or 4s and see how that does and if you still need more then move up. It will be super powerful with either one. The more lipo cells you go with, the lower the Kv motor you will need to avoid burning up your hardware. And make sure the motor is also capable of handling the amount of cells youre trying to push. What are you using it in?