I have recently resumed futures after a lenghty layoff. I have limited myself to these 2 instruments. It is somewhat predictable when there wil be more volatility in both of these.
Crude inventories are released on a schedule and the day before there will be unusual activity. Also weather and political events will give reason to take notice. On the last trading day of 2006, when it was announced that Saddam Hussein would be executed, QM jumped about .50. Shorting this "non-event" would have worked well, very well, or if you held for this week, perhaps a life changing event.
ES also has days when volatility is predicatible. Unemployment, Fed meetings (and minutes of them), PPI, CPI, GDP, ISE, Beige Book, Retail Sales are all worthy or notice and a special strategy should be anticipated if trading in front of or after the release of these numbers.
So, my answer is both, when the time is right. Hope this helps.