Two party system is terrible and both options are ridiculously bad, but you are crazy if you think that they are the same.
Should we break the system and make a new one? Yes. Will you do anything like that? For 99% of people the answer is no.
So if you are doing nothing to change the system, at the very least you should do what you can within the system (ie voting)
Anyone who says "both sides are terrible so why bother" but does nothing except online bitching, is just letting the people who are voting decide the future for them. If you are doing nothing to fight the system, at the very least use your rights within the system to choose the least awful option.