Any other action is just going release the chemicals in slightly different but similar ways. So using your logic, why is being a selfish hedonist going to be better than the first option? You have just given a somewhat nihilistic argument that neither outcome matters.

Meanwhile, have you tried both ways? My personal experience suggests that acting benevolently to others is much less stressful, makes one much happier, and that leads to better physical health even. Compared with being a bitter curmudgeon on the other extreme, you will likely be happier and live longer. It's a much better way to release the chemicals.