May I ask why YM now appears to be your primary contract of the stock indices? How would you characterize their differences intraday?
I'm sure there are more similarities than differences, but arguably enough differences that it could matter and where particular strategies may not work across all three.
I cut my teeth some decades ago with YM. It holds a special place in my trading psyche.
The granular YM tick (1t = 1pt) imo, offers a great opportunity to hone skills. I have luv/hate periods regarding the exactness. In any case, the exactness is unlike the other US index products which move in fractions of a point, and are not equivalent to the movement increments of the underlying cash index.
As you know, my methods are volume-centric. In the case of futures, volume is centralized, therefore as long as sufficient volume exists in the trading time-frame, my methods are applicable. What is "sufficient"? That leads to a mention of volatility which is outside the scope of this post.
Bottom line for me, for now... YM is a happy place.
Thanks for asking.