Answer 1

I'm not quite sure if that's what you mean, but I'd say
a = a
is the simplest tautology while
a = not a
is the simplest contradiction
in a rather general sense.
If it's about reasoning it would be quite similar:
a → a
would be tautological while
a → not a
would be a contradiction.
If it's more about the outcome, a tautology simply means, it's always true. So "True" (TRUE, true, 1 or whatever, depending on language or field) would be the simplest tautology value wise, while "False" would be the simplest contradiction by the opposite line of reasoning.