which economic news has the most impact on forex?
I think interest rate decision news has the greatest tendency to move exchange rates. I have seen exchange rates start moving based on pure anticipation even before the interest rate decision is made by the central bank.
Whenever a country's central bank cuts interest rates (healthy economies only), their currency weakens. For example, the United States is expected to cut interest rates by around 25bps tomorrow and we are already seeing the eurusd exchange rate skyrocket to 1.1800 (meaning the dollar is weakening against the euro) even before the announcement has been made.