I do believe that the primary goal of the government is still to increase the wellbeing of people. It's a complex machinery. Even if most politicians are corrupt, the whole thing can still strive towards the good. Corporate influence and corruption go against it while decomracy and separation of powers go for it.

However

The question was if it cares about MY best interest. The answer is no. The very purpose of the government is to limit all individuals' freedom for the greater good. Take stealing as an example. It would be in my best interest if I were allowed to steal. But that would still suck if other people were allowed to steal from me as well. If we all agree not to steal from each other, it will be even better for me (even though, individually, I would still be in better position to be able to steal when everyone else is not). So it's not so much about MY best interest, as it is the society's.