If one does have an edge , any good instrument would suffice , but if positive expectancy isn't there then any type of instrument will be doomed for failure in the long run.By the way its always best to diversify optimally so that risk is minimised , otherwise there is no such demerit in trading only Nifty ( I assume its Nifty futures only. but if someone trades nifty options along with futures then it is a diff ball game )