There is tax differential in US. ES is subjected to 1256 contract rules, so taxed 60% long and 40% short term gains taxes, where as SP500 ETF if held for a year (typical buy&hold) then it is taxed at 100% long term gains rate.
Based on their tax rate, it could be big difference.
Even other-wise, it does not make sense to buy&hold ES over SP500 ETF
* SP500 etf can be bought commission free in most brokerage houses and it costs 3-4 basis points.
* SP500 etf can be invested regularly when ever they get pay checks, ES investment is lumpy
* SP500 etf buying can be set and forget (most brokerage houses allow automatic buying in some fixed dates), where as ES has to be rolled quarterly based on optimal dates and times
* Buying ES and keeping rest in cash is not same as buying SP500 ETF. In ES you are paying implicit interest and you are not getting any returns in cash. One could mitigate this by buying Treasury bill ETF. Then they could as well buy SP500 etf. Bills have other problem like paying ordinary income tax which is taxed at higher rate
Only disadvantage SP500 ETF has over ES is dividends. Dividends are taxed at higher rate, but SPY dividends are only 2%. These dividends can be sweeped quarterly to reinvest in ETF if desired or they can buy Muni bond ETF which mitigates tax concerns.