Historically the equal weight S&P 500 index has outperformed the traditional S&P 500 index. However, due to the higher turnover associated with the equal weight index, the small advantage may disappear. Which ETF tracking the equal weight S&P 500 index has the longest history so I can use it to gauge the impact of transactions costs.
You are right, the Equal Weight performance advantage has disappeared over the last couple years, but not due to the reason you think. Both the Equal Weight index (RSP) and the regular S&P (SPY) are rebalanced once per quarter so there is not much difference in the turnover costs. However, when the larger capitalization stocks such as Apple, Microsoft and Tesla outperform the rest of the market it helps SPY. When smaller cap stocks outperform, it favors RSP. I second @nooby_mcnoob with RSP.
Note that the "Equal Weight" aspect only applies at quarterly rebalancing time (close of business on the third Friday of March, June, September, and December) - it's not a daily rebalancing. This is the same schedule as the standard free float market cap-weighted index. So there may not be any significantly "higher turnover" for the equal weighted-based ETF versus the standard ETF. There's only one S&P 500 Equal Weight ETF trading in the US: NYSE Arca:RSP Invesco S&P 500 Equal Weight ETF started trading 2003-04-30 This also appears to be the longest-running equal weight ETF listed against any index, with Nasdaq:NQQEW (First Trust Nasdaq-100 Equal Weighted Index ETF) the next longest listed, starting 2006-04-25. Incidentally, Norgate's S&P 500 Equal Weight index ($SPXEW) and S&P 500 Equal Weight Total Return Index ($SPXEWTR) daily data goes back to 1970-12-31.
%% THATS sort of the way i see it also \LOL; it disappeared from my trading notebook. Not much volume but that's ok sometimes with other ETFs