[kimchi]

It depends upon what type of trading you want to do, and what you mean by 'tougher'.

Commodities trend better than stocks, so if you are trading trends it will be easier with commodities.

Volatility isn't so important from a risk perspective as you can reduce a volatile market to having the same risk on your portfolio as a docile market through good risk management and position sizing. I think volatility becomes more important when you shorten your time horizon. Trading a slow stable market isn't going to yield much, but will generate proportionately more trading costs.