Not voting for the third party you believe in is the greater sin (IMHO) as garnering 5% of the popular vote makes them eligible for matching federal funds in the subsequent election.
Simply put, let's say you're a Libertarian, but don't want to vote for Gary Johnson to prevent 'throwing your vote away'. But voting for him now possibly adds to his campaign funds in the 2016 election, which increases third party viability fairly substantially.
Simply put, let's say you're a Libertarian, but don't want to vote for Gary Johnson to prevent 'throwing your vote away'. But voting for him now possibly adds to his campaign funds in the 2016 election, which increases third party viability fairly substantially.
http://en.wikipedia.org/wiki/Matching_funds#In_politics