For lack of a better option. I left Brazil, so I don't vote anymore, but had I still been there, I would probably have voted for Dilma even though I'm strongly against her party. She was the "least worse" alternative.
Yes, voting is compulsory (required by law) in Brazil. Citizens can also cast a null/blank ballot if they feel that the candidates on the ballot should not be elected. Despite this, only 76% of citizens actually voted in the last presidential election. 69% of the population voted for one of the candidates, only 7% voted null/blank. [1]