First let me reiterate that there's nothing wrong with trading the YM. I would do it, if necessary. My view is it's the kid brother of ES in every way.
As for "capturing" the bid/ask spread in YM versus ES, that is a pure fallacy. In order to realize $$ benefit from entering limit orders at or inside the spread, a trader must likewise exit that trade <b>at the exact extreme tick</b> of the given swing's end.
Think about it. If you enter YM long at 13400 on a limit order when bid/ask is 00/01, you essentially bought the bid. That very seldom happens in ES, granted.
If you likewise exit that trade at 13420 and price action goes one tick further beyond there, what happened? You just lost the spread. You accomplished absolutely nothing. The same exit at 13421, 13425, 13440 would have yielded the same +20pts if your entry was likewise higher than 13400.
Make sense? The only way anyone ever "captures" the bid/ask spread is by exiting to the exact extreme tick before reversal more often than not. Who amongst us does that? Nobody.
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As for different tick selections for protective stops. Every once in awhile, the ES will stop out at -4 ticks (-$50) whereas the YM will hold a -10pt stop (-$50) by a single tick. That in essence made buying the bid worthwhile.
For every instance that happens, ninety-nine other trades will see the stop taken out by more than the extreme tick. These days, stops are usually taken out by a country mile. Unless a majority of trades in YM hold by one tick whereas as majority of ES trades stop out by one tick, the whole basis of stop management one versus the other is moot.
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Big picture: when one symbol moves $50, the other usually does to. If that weren't the case, they'd be arbed to death for free money in great size.
All the nitpicky minutae between YM and ES, which one is better is the wrong rabbit trail. Serious pro traders prefer the ES because in essence it is identical to YM and offers unlimited trade size. I commonly turn 10 - 20 ES contracts per trade, and will turn 50 - 100 contracts per trade soon. That's not possible in YM without slippage, which then totally negates bid/ask argument.
The ES used to trade 2x - 3x ES dollar range per day. That spread has narrowed and in many cases disappeared. So went the advantage of ER over ES.
The YM is smaller than ES, therefore nicely suited for small-lot traders. No question there. At some point in time, pro traders will need to clear more than 20 contracts, especially with managed accounts. If they are growing, they will quickly outgrow the YM.
Whatever works for ya, go with. We can lose money with any of them!
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