The Republicans have lost any credibility at all with their unwavering support of that fiasco in Iraq. Additionally, they are turning into a part of religious fanatics (aka bible thumpers) and that is scary to most of us intellectual minded people.
My main beef with the Democrats is their soft approach to the illegal immigration issue, particularly in supporting amnesty which is just ridiculous in my view.
So, independent party or libertarian candidates are the only choice on principle but they have no chance to win so as usual it will be the lesser of two evils.