That depends on your broker and what they require for risk and margin. Also, cost can vary from broker to broker. I like it that ES has longer trading hours but I find many traders make poor decisions in the middle of the night. Trading during liquid hours with more information might be preferred.
The leverage of Spx (4.725 x100) is bigger than ES‘ leverage (4725 x50). But this is not so important because you could trade 2 ES slots. The downside risk of options is capped by the premium. My question is if you participate more on Spx options when the index shows some momentum. I refer to increasing volatility and gamma.