Best? Kirk and Balok. Both are playing chicken. Kirk opens the door for cultural exchange.
Honorable mention for Picard's damage control with the Malcorians. The Federation's policy of secretly spying on other cultures before diplomatic overtures gives concerns regarding their ethics.
Worst: Has to be the bureaucratic bungle that agreed on a border containing habitable worlds within the De-Militarized Zone between the Federation and Cardassians.