What is the most effective response to aggression-appeasement or collective security?

In the context of World War II, including the years just prior to its outbreak in 1939, the historical record is generally quite clear: the most effective response to the aggression of nations such as Germany and Italy during the 1930s would have been collective security -- galvanized by the will to take military action when necessary. While appeasement proved effective in buying time for Allied preparations for war, it did so at the cost of territorial losses, betrayal of national sovereignty (in the case of Czechoslovakia), and a strengthening of the aggressor-nations.