If the election for President was based completely on the popular vote, by far most of the attention from the parties and the candidates would be spent on the large states, California, Texas, New York, Florida, Pennsylvania, Illinois, Ohio, Michigan, Georgia, North Carolina, New Jersey.
The problem with this argument is that, under the current system, candidates limit their campaign to an even smaller circle of "swing states" while ignoring the rest of the nation, including most small states like Wyoming and Vermont where the result is more or less predetermined. The electoral college doesn't force candidates to pay attention to these states because most of them heavily favor one of the two major parties. Under a popular vote system, it might make sense for Democrats to campaign in South Dakota or for Republicans to campaign in Delaware, because the votes they win there would contribute to a national majority even if they end up loosing the state. The current system, however, penalizes those who campaign in states they are unlikely to win and rewards those who focus on a handful of the largest and most competitive states to the exclusion of all others.
It is likewise important to note that the electoral college supplements the voting power of the small states by taking votes away from states where more people live. If electors were distributed proportionally according to population, a state like Wyoming would have a single electoral vote; instead, the current method of allocation awards it three votes, then makes up for this extravagance by disenfranchising Texas and California (both of whom are underrepresented in the electoral college). The result: a Wyoming ballot is effectively worth three of it's Californian counterparts. For all the impassioned defenders of the electoral college, I am yet to meet one who could make a reasonable argument for why some citizens deserve more representation than others.
