Which is the most profitable?
You ask for the "Best Trading Instrument" in the title, and "the most profitable" in the post...the best and most profitable are not necessarily easily matching or congruent.
I only know options. So I'm bias and partial to options. that's my answer.
The "Best" thing to trade is obviously very highly subjective from person to person;
The "most profitable" is much more closer to being a linear answer,
Options are leveraged products...it doesn't take that much money to have potentially great rewards.
(but like everything in life...the devil is in the details)
Everything stems on your ability to predict the market. Only this matters.
The
Future...
predict it; whether that be 1 minute, 1 hour, 1 day, 1 week, 1 month, 1 year from now,
If you ask me, it's easier to predict and/or manage...things on an intraday time frame,
Beyond this, the future is essentially just a big unknown shit storm with way too many variables beyond your control, to foresee and grasp,
Controlling or managing variables...is key to winning in the market,
If you don't got this...you're just a fool. with his money, to be soon parted.
Reasonable expectations unfolding and happening -- not simply gambling blindly,
...if you want to treat the market like a casino...then you will get casino returns -- which is leaving with an empty wallet.