ETFs for long term investment

I have long term investment strategy and have identified top performing ETFs as slow and stable gain option. I am now realising it is better to diversify. Hence, I have invested in Aus and US market. While AU ETF have provided me with decent return this month, I am still in loss in US market, yet profitable overall. I also think using paper trading account and only investing amount that you are likely to invest in reality provides the best way to test your investment strategies and thus find the best strategy which you are able to withstand risks associated with investment.  Best wishes to all.