The SPY has dividend payment adjustment that makes the long timeframe charts far from perfect; also many times irregular bad prints that screw with analysis.
The ES has rollovers so suffers from the same problem, even if your data feed provider does back adjustment do not trust it for long timeframes as every provider use different backadjustment methods.
Although it is true that SPX updates slowly intraday for long timeframe analysis it's the preferred one because it's continuous.
Case in point ?
Use ES for intraday, afterhours, some weeks at most.
For everything else, use SPX.
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