Different moves in each stance can be Big Shot.
They are usually Unblockables or Lifts but NOT always.
Guard Breaks are ALWAYS Big Shot.
Not all kicks are Big Shot as well. R1 + Square is always Big Shot but Jump Square is not.
Some styles have kicks in their moveset. Some are Big Shot some are not.
So it depends on stance.
Only guarantees are R1 + Square and Guard Break. And every stance has at least one guard break (Jump Triangle)