It seems that ym has a smaller spread than es .1 vs .25, so it should be cheaper to trade, but the volume on es is much higher. Does anyone know the reason
I'm not sure why every one keeps talking about the spread like it's a cost. Even if it were then the YM would not be cheaper using that metric. With the YM you'll find your stop getting busted through, and often times the spread will widen. The SandP 500 is the leading world index, so I assume that's why it's traded more. The liquidity of the ES means that your stop will not be busted through, and during market hours it's very rare for the spread to widen. Anyway, if you use a limit order, then there is no spread at all. Even though the YM is 10 ticks per point, if the ES moves 1 point, the YM will typically also move 1 point or 10 ticks.
The minimum tick fluctuation in the YM is 1, not .1 During regular trading hours it is unlikely that you will see a spread > than 1 tick. You will not have to worry about any of this though from your standpoint. You don't have enough money to influence the market if asking these questions.
Ym is more whippy and lower liquidity makes it easy to be shoved/overshot. Yes you have 10 entry exit points per $50 rather than just 4 per $50 in ES but if you put them side by side, ES will often produce more range to capture.