What is the most common way amendments to the US Constitution have been ratified?

All but one Amendment to the US Constitution has been ratified by state legislatures (3/4 of the states must vote to ratify). The 21st Amendment, which repealed the 18th, was ratified by conventions in the states rather than the legislatures. Congress chose this method primarily because it was thought that state legislatures could be influenced or intimidated by Temperance Movements to vote against the Amendment, which repealed Prohibition of alcoholic beverages in the US.