This question already has an answer here:
Some US ETFs (Vanguard, iShares) that I am interested in are traded on several exchanges, typically including NYS and ASX. I live and pay taxes in Australia. Does is make any difference if I buy the stock on NYS or ASX? Is one of the options better? Taxwise it seems to be the same as I am still subject to 15% witholding tax from dividends paid by the US company in both cases.