In your opinion, which index is the best for intraday-trading?

During NY session: Dow, Nasdaq or S&P 500?

During Asia: Nikkei225 or Hang Seng?

Hi,
in my opinion during NY better trade Nasdaq (more predictable);
during Asia - Nikkei (less volatile and more thending).

It depends what you're trading (CFDs, Futures or Options).
I mostly prefer the NQ100 for intraday plays/"scalps, swings" and the S&P500 (overall and very specific moments for Options plays with huge potentials).

If you're scalping the NQ100 you really have to get familiar with the whole index and its true nature, how, when and why.
Initiation moments are THE absolute key for real success, every intraday-movement has a very specific pattern (some tools are extremely helpful to see it in front of your "eye" and know why the chart is formed).
Often there is a clear advantage in which direction it will go and even when there are reversals incoming.

I also prefer the NQ over the Dow because the correlation with the SPX is a bit higher.

But trading the Dow wouldn't be a problem either.

SPY |SPX | S&P 500
Reason: Availability of data for Statistical Edge and disciplined comparison to NAS100