[gergery]

The key principles are 1) how many decisions must you make, 2) what is the cost of a wrong decision, and 3) how much information do you have to make your decision on

So,
What game can least be played with a formulaic strategy?
Probably some version of 7 card stud, since with more information available and more streets to make decisions on, there would be more rules (ie. formula) needed.

What game is most difficult to teach?
Probably Pot or NL holdem, since so much of your success there relies on hand reading which is situational and opponent dependent. Obviously, hand reading is critical at all forms of poker, but the value you can get from good hand reading is much higher in pot limit/NL games. And putting your opponent on a hand range based on many viewings of their hand is more difficult. And hand reading seems more difficult to teach than any other poker concept I can come up with.

I’d also think cash games require more talent than tourneys, short-handed requires more talent than full-ring, live requires more talent than internet, pot limit requires more talent than NL which requires more talent than limit – due to the principles above.

-g