HSI is the best trending instrument, day-in and day-out in the entire world. It's been that way since 2003. Or, you can trade the highly correlated HHI. It's like trading a 1/2 HSI contract. Both have mini contracts which trade at 1/5th the price per tick. The big contracts trade at $6.37 USD per tick. The minis (MHI and MCH) trade at $1.27 USD per tick. Good news for U.S. traders is that the USD is pegged to the Hong Kong Dollar (HKD). This means that there is no currency risk involved as money is moved back and forth between the two. "HSI maybe ok" (dozu888) Seriously? Dude, it will steal beats from your heart.
I don't trade it the same as the day, it has different behaviours. I always enter by limit order and it is never so dry you get problems there. I was talking to a new trader recently who thought anything less than a half million in daily volume was 'untradeable' I started on some very lean months on the US indices so it all looks like gravy to me.
As wrdtrader said, "best" is relative to the moment. Presumably, your question is relating to scalping/day trading so volatility favours longer-term direction? if that's what you're asking, I'd get a good grasp on the behaviour of all the HSI, NIK225, DAX, DOW, NDAQ and trade the one with the highest volatility at the time while keeping an eye on the others, switch when the current choice runs flat. Having the 5 charts on screen together can easily show you which are moving and which are not