As someone who's traded just about everything at one time or another, here's my take on emini futures:
They are easier to trade than most other futures, tougher to trade than stocks. Commodities are erratic... and too illiquid for short-term trading other than gold, oil & currencies.
Stocks require research to either find what's moving right now or find the next one to "marry" when prior darling goes dead. Very few stock traders stick with same symbol(s) day in & out for five years straight.
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The ES is deceptively easy/hard to trade right now. It is all about volatility, or lack thereof. When intraday ranges average greater than 10pts on average, potential to take 2 - 4 of those points from swings most day is rather simple (never easy).
When intraday ranges hold within 6pt or smaller ranges intraday, it's much harder to hit the profit goal while stops are easier to be taken out. Why price action remains in the stop zone area much longer. Normal to wide-range days move away from initial stops, and give opportunity to profit.
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The only reason I would/do trade the ES is managed money efforts. As an individual trader, the ER with five contracts will outperform ES with twenty contracts most given days. It is far easier to average +$100 daily in ER than ES, because ER intraday dollar per contract range is 200% to 300% that of ES with more numerous price swings to boot.
More volatility is a good thing... usually. The ER offers greater profit potential, but can be spiky & erratic times. It is not an easy ride, but once mastered is the best emini for retail traders profit-wise.
The YM seems to trade much smoother than ES, based on system analysis studies. Less noise in YM than ES... easier to hold stop loss orders on the way to profit objectives.
BTW... there will often be serious slippage orders in ES at 1,000 contracts entered at once. During low volume periods of a session, 1,000 contracts will slip one point or more. If that's when you need to exit, the market won't accomodate your decision.
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Eminis require extreme patience and discipline. When volatility is normal to high, profitable trading seems easy. When volatility is low, impatience and frustration set in. Pressing for daily $$ goals and/or "revenge" trading out of anger emotions wipes out more emini traders than anything else.
Individual traders just learning the game may best look to the YM or better yet, NQ... the smoothest (trendy) emini of all. More volume and open interest than YM as well. Lots of pro traders are there, too.
More experience = skilled traders gravitate to the ER, which tends to eat up beginners early & often.
As for the ES? It offer zero advantages over these three other emini symbols except for size. Any successful ES trader can take their skills, adjust them slightly and do exceptionally well in the other emini symbols.
The reverse is not necessarily true... ES is by far the toughest emini of all right now, solely because of low volatility period in time. When the VIX begins to trend higher (it will) the ES will become much easier to trade.
Best Trading Wishes